Node.js Flashcards

Question

**What** is the **path module**? (**Hint**: Paths are used in URLs to specify file locations)

Answer 1

Built in **node module** **better** than working **with strings** **useful methods** for working with **paths**

Answer 2

**Built** in **node module** **gives** us **information** about **current operating system (OS)** **os.freemem()** - gives free memory **os.totalmem()** - gives total memory **os.uptime()** - up time of computer **os.userinfo()** - current user information

Answer 3

Node **built in module** **always** **prefer to** use **asynch methods**

Answer 4

A **signal** that **something has happened** in **our application** **node's core functionality is built around handling events** **(EventEmitter)** **Ex.** **HTTP listening to port**, client **request incoming**, **raises event** application **reads request**, **returns** right **response**

Answer 5

adding **additional arguments** when **raising an event** can **pass data** about **event that just occured** listener **can recieve data** (event arg) and **call url, log, etc**. **event arg best practice** - encapsulate in obj

Answer 6

**Not directly** **create a class** with all **capabilities** of **EventEmitter** **use** this **class in application**

Answer 7

**One** of the **powerful building blocks** of **node** ex. create **webserver** that listens for **HTTP request** **can create** backend for **React or Mobile** **However...** **In real world, we don't use HTTP module** **Why?** As we **add more routes**, **code get's complex**, added **linearly in callback function** **Use express instead** (**built** on **top of HTTP module**)

Answer 8

A **command line tool** and **free open-source** **registery** **for third party libraries (re-usable code)** **any functionality for an app**, **most likely** **a free open-source library (package)** on **NPM registery** **1 million packages** **11 million developers rely on re-usable, open source tooling** **Share?** **Can create and add to NPM**

Answer 9

1. **First**, checks to see if the **module is in the node core** 2. **Next**, checks to see if the **module is in a folder/file** in the project 3. **Finally**, checks to see if the **module is in the node\_modules** folder

Answer 10

**Package.**JSON **updates** dependencies

Answer 11

exclude node\_modules **Why?** It could be hundreds of **megabytes** in size (large) everytime someone **checks out code, have to download** **Soln?** **package.json** stores all node module dependencies can use npm to instal dependencies locally!

Answer 12

**Create** a .**gitignore** file

Answer 13

Ex. mongoose **4.13.6** **major version** add new feature that could break existing apps dependent on old version **minor version** adding new features, API not broken, increase minor **patch release** bug fixed, increase patch version

Answer 14

**It tells node...** download the **current module\_package** as **long as the major version** is **the same** (no breaking changes will occur) if **newer minor or patch version** is available, will **download** Ex. Built application using **mongoose ^4.13.16** **six months later,** someone **checks out code from repository** **downloads dependencies...** **newer mongoose version available** **4.14.0** (as long as **same major version**) new minor and patch will be **downloaded/installed**

Answer 15

**Tells node** to **download the dependent module** with... **same major version** **same minor version** **updated (newest) patch** **version**

Answer 16

**Sometimes** in **real world,** **new patch versions break previous versions** To ensure **exact module versions** are downloaded... remove **~ or ^** from **dependencies in package.json**

Answer 17

Terminal... ## Footnote **npm list (shows all dependencies)** **To show only your app...** **npm list --depth=0**

Answer 18

returns **package.json** for module **can also go** to **package registry (npm registry)** check dependecies look for current versions

Answer 19

Ex. npm view mongoose depencies

Answer 20

**Get versions**: \> npm view packagename versions **Downgrade/upgrade:** \> npm i packagename@major.minor.patch

Answer 21

**Terminal:** \>npm outdated \>npm update \*\*only **minor and patch** versions updated How to get major releases? \>download npm-check-updates

Answer 22

\> npm-check-outdated (ncu) \> ncu - u (update) \> npm i (install)

Answer 23

**App dependencies** required for our app to function properly **Dev Dependencies** **used during development process** (**testing, analysis, bundling code**) \*\*should **not go in production environment** where **APP deployed** **\>npm i jshint --save-dev** **package.json** will segregate devDependencies and appDependencies

Answer 24

\> npm **uninstall** packageName or \> npm un (uninstall) **package.json** updated and **node\_modules updated**

Answer 25

**\>** **npm login** \> **npm publish** **Success!** **Now, use in another project** **\> npm i package** **\*under dependencies in package.json**

Answer 26

specify **version update** (major, minor or patch) **npm** will **update version** Ex. npm version minor v1.1.0

Answer 27

We **don't want** to **hardcode if statements**

Answer 28

**Introduced** by **PhD student as his thesis** a **convention** for **building HTTP services:** (**CRUD**) operations: **Create, Read, Update, Delete** \*expose resources on various endpoints (customers list)

Answer 29

client (front end) sends **HTTP requests to server** (using HTTP protocol) to save data, store data, access data

Answer 30

Every **HTTP request** has **a verb that determines intention** **Application exposes resource** **using meaningful address** **get resource, add to resource, delete from resource, update resource** **GET** getting data Ex. GET /api/customers to get list of all customers response will be an array of customer objects **POST** creating data POST /api/customers post new customer to collection include customer object in body of **PUT** updating data PUT /api/customers/1 include complete customer object in body with updated properties server updates this customer object in customer resource **DELETE** deleting data DELETE /api/customers/1

Answer 31

**Express** is **most popular framework for managing routes** **Fast, lightweight and perfectly documented** **Why?** As we **define more routes**, we have to **add more conditional statements** A **framework** like **Express** allows us to **add additional routes** while **keeping our code clean and maintainable**

Answer 32

**We don't** have **if blocks** define **new routes** using **app.get**( ) can **move routes** to different files **Express** gives our **app a skeleton** (**structure**) Ex. can **move all routes** for **courses to courses.js**

Answer 33

**a variable** that is **part of environment process runs** value is **set outside of our application** Ex. Port environment variable **Process** is a **global object with env** **Why?** In **real world**, port is **dynamically assigned** based on **hosting environment** Cannot **hard code it** and **expect port will work**

Answer 34

**essential (required)** values **passed with a route** Ex. Get **all posts** from **a** **given year / month** **Server** - /api/posts/:year/:month **Client** - /api/posts/2020/08

Answer 35

**Additional data** sent to our **server in HTTP request** Used to **provide additional data** (optional data) to **backend service** **Stored in a query object** **Ex.** /api/posts/2020/02**?sortBy=name**

Answer 36

app. use(express.json()) app. post

Answer 37

**Always validate client input** **NEVER EVER** trust what client sends Soln? **NPM Joy**

Answer 38

An **NPM package** that **simplifies validation of client POST requests** **How?** **provides a schema (how many chars, input allowed, etc.) for POST requests** **Why?** Don't want to validate client input at the beginning of POST request

Answer 39

**an error object** **too complex to send to client** instead, access error message in the object .error.details[0].message

Answer 40

Look up data If not exists, return 404 validate client req if invalid, return 400 update data return updated data to client

Answer 41

**Middleware** function that takes request obj **returns response to client** or **passes control to another middlewear** **function** core concept in Express **Configuration** storing configuration settings and loading for different environments **Debugging** debug package in node.js **Templating Engines** returning HTML markup to client (vs. JSON) **Pug, Mustache, EJS** Generating dynamic HTML to return to client

Answer 42

An essential **concept in Express** Express includes **pre-built middleware** Can create **custom middleware for request processing pipeline** (every request goes through request processing pipline) Ex. logging, etc. **MIddleware function** takes a request obj AND terminates req/response cycle by returning response to client OR passes to another middleware function Ex. app.get('/', (req, res) =\> {})

Answer 43

**In sequence** Ex. First logging, then authentication

Answer 44

# **Define custom middleware in a** separate **module** Import (**require()** ) and install (**app.use()**) **Why?** **clean** **code practice**

Answer 45

Express.js **pre-built middleware** But every **third party middleware** used will **decrease performance** (**request processing time**) of **application**! So **use wisely and sparingly** **Best Practice Middleware?** **Helmet -** helps secure application **Morgan -** log http requests

Answer 46

**NODE\_ENV**=Production

Answer 47

**Used** for setting **configuration settings** - **production, development, testing** **can store config settings for appliction** **DO NOT:** **application secrets** **password of database or mail server** **that password/secret is available** **WHY?** **Check into repository, everyone can see** **SOLN?** **Store in env variable**

Answer 48

export app\_password=1234 **custom-environment-variable.json** (file)

Answer 49

**Used** for **debugging** can **set various environments** for **debugging** **when** in that **environment**, only **debug messages** from that **environment shown** Ex. **export DEBUG=app:\*** (get all debug environment variables)

Answer 50

**Servers** often return **JSON objects** **sometimes** need to **return HTML** markup to **client** **Templating engines** help us **generate dynamic HTML** / **return to client** **Popular**: **PUG** Mustache EJS

Answer 51

**Don't write** all code in **index.js** **First**, create **a folder** called routes, put **route logic** for **each API endpoint** **in a separate file (module) in this folder.** **Import each module in index.js** Ex. **courses.js** and **home.js** which **contain all the logic** for the **routes to courses API** and **home API** **Second,** create a **folder** called middleware and move logic for custom middleware to this module

Answer 52

**Head over** to **Express.js** and **view their docs** on **database integration** **Mosh** covers **mongo and mongoose later** in the **course in depth**!

Answer 53

It's **NOT a part of Express** **authenticating users** to **access API endpoints** is **covered in another module**

Answer 54

Asynch **does not mean** concurrent (**multi-threaded**) single thread **executes first line**, schedules **next task for future** returns to execute **next line of code** returns to **complete task** Ex. **Single waiter** in a **restaurant** (single thread) takes order, **doesn't wait in kitchen** for cheff only **one waiter** (**not multithreaded**)

Answer 55

**Callbacks** a function that is called when the result of an asynchronous operation is ready. **Promises** **async and wait** syntactical sugar over promises

Answer 56

**a function** that is **called** when the **result of an asynchronous operation** is **ready**. **When** the **result is ready**, **call the result** back **using a function** **Why?** Cannot **return a value** from an **async function** (it's undefined until task complete) Must use a **callback** to call **result when it's ready** Ex. Call the **user object back** when **result is ready**

Answer 57

Nested **callback functions** **Solution?** flatten structure of the code replace **anonymous function** with a **name function** second arg to callback is **anonymous function**

Answer 58

**Nested structure exists** because **second arg** to callback is **an** **anonymous function** **Soln?** flatten **structure of the code** replace **anonymous function** with a **name function** **Best?** Use promises

Answer 59

**extremely powerful** when **dealing with asychronous Javascript** code **an object** that **holds the eventual result** of **an asynch operation**

Answer 60

**Pending** **initially** when we **create a promise object** it's in **pending state**, then it **kicks of an asych operation** **Fulfilled** **asynch operation** is **completed with a value** **Rejected** if something **went wrong during execution** of asynchronous task, result will be **an error**

Answer 61

**Promise** is an **object** that holds **eventual result** of an **async operation** **Initially**, it's in the **pending state** if the **result is completed**, it **moves** from **pending** to **resolved (fulfilled)** **resolve - sends result to consumer** if there is **an error**, it **moves from pending to the rejected** **reject - returns an error to consumer**

Answer 62

Modify **callback functions** to **return promises**

Answer 63

**Promises** expose .**then ( )** method can **chain to create complex asynch operations**

Answer 64

**Promise.reject()** **Promise.resolve()**

Answer 65

**Single thread** kicks off **multiple promises at same time** **not waiting** for **result of first asyc operation** to complete kicking off next **asyc operation right away** **Waiting for ALL promises to complete** **returns an array** **If any of our async operation fails, final promise is considered rejected**

Answer 66

**Promise.race()** As soon as **one promise in array is completed**, promise at **end of race is considered resolved** **Promise resolves** as **soon as first promise resolves** **Final Result is value of first fulfilled promise**

Answer 67

**await the result of a promise,** **store it** and **pass it to another async function** **Why?** It's **cleaner and easier** to **understand** than ***callbacks* and *promises*** **Remember:** **Whenever** you use an **await inside a function** You **must decorate the function** with the ***async* keyword**

Answer 68

**Syntactical sugar** over **Promises** **Allow** us to **write async code** that **looks sync** **Built over promises** **JS engine** converts our **code into Promises** Code **looks synchronous** but **it's executed asynchronously** the **JS engine** executes this **code asynchronously** **await releases thread to do other work** **Code still runs async** **looks synchronous** **errors are caught using try/catch block**

Answer 69

**MongoDb** **noSQL database** **Why?** A very popular **database management system** **Often** used in Apps built in **Node and Express** **Expert?** **MongoDb requires it's own course** **learn enough to get the job done here**

Answer 70

A very **popular database management system** **Often** used in **Apps** built in **Node and Express** **How different?** **No rows, columns** **no schema or database design** **simply store JSON objects in MongoDb** **Query MongoDb get JSON objects** **Simply, return JSOB objects to clients**

Answer 71

https://**stackoverflow.com/questions**/57856809/installing-mongodb-with-homebrew \> **brew** tap **mongodb/brew** \>**brew** install **mongodb-community** **\>brew** services start **mongodb-community** **Create directory:** \> sudo mkdir -p /data/db **store mongodb data** \> sudo chown -R `id -un` /data/db **intialize mongo** \> mongod **deamon listens in background for port connections**

Answer 72

A **client application** to **connect** to a **mongodb server** can **look** at **database** can **work** with **our data**

Answer 73

Using **Mongoose**

Answer 74

**Collections and Documents** Collections **Document** each document is a container of key value pairs Mongoose schema defines shape of each document

Answer 75

Helps us **define the properties (shape)** of **each document** ## Footnote **Mongoose.Schema( { object } )** **object passed defines key value pairs for each document**

Answer 76

String Number Date Buffer Boolean ObjectID Array

Answer 77

Create **a document** Store **in MongoDb**

Answer 78

Can **filter, limit number of documents**, etc.

Answer 79

.**find** **(** { **key**: **{ }** } **)** pass an **object** for the **value** in a **key, value** pair **eq** (equal) **ne** (not equal) **gt** (greater than) **gte**(greater than or equal to) **lt** (less than) **lte** (less than or equal to) in **nin** (not in)

Answer 80

.**or** ( ) **pass** an **array or filter objects**

Answer 81

**.find** ( ) pass an object with (**key, /pattern/**) **^** starts with (start of string) **$** ends with (end of string) **/i** make not case sensitive .\* zero or more characters present

Answer 82

**.skip** ( (pageNumber - 1) \* pageSize ) **.limit** ( pageSize )

Answer 83

.**find** ( ) .**sort** ( ) .**select** ( )

Answer 84

**Query First** - We want to validate permissions **Update First** - Just want to update directly Ex. Update **Likes in DB** without returning **Post object**

Answer 85

**wrap** in **an object** **name**: **{type**: String, **required**: true**}** validation **kicks in at the time** we **try to save a document** **Remember... Validation implemented on Schema properties are only meaningful in Mongoose** **MongoDB doesn't care about validation logic implemented in Mongoose** * *It doesn't implement validation at Data Base level like SQL** * *So...** **Validation code is only meaningful to Mongoose** **Mongoose runs validation logic when we try to save a document,** **if document is not valid,** **it will not save it to the database**

Answer 86

We **should use both** **Joi in RESTful API** to make sure **data client sends is valid** Still **need to validate data** to **ensure it's in right shape** before **saving in our database** **This** is a **two pronged approach** to **avoid programming errors**. ensuring **validation logic in mongoose**, ensures we **don't have programming errors** Ex. Get a **valid object from client**, **forget to set** req.body.name **to** **Mongoose.Schema.name** **Joi** - **validates** **data recieved** **from** the **client** **Mongoose Schema Validation - validates data before saving in database**

Answer 87

**Ex**. **Price** is **only required** if **course** is **published** ## Footnote **add required validator in an object** **return a boolean from required function** **Cannot use =\> and .this** **Why?** **Because =\> .this references enclosing function** **function ( ) { .this} references current object**

Answer 88

**Number** min, max **String** minlength, maxlength, match, enum

Answer 89

**Use promises!** callbacks depreciated **isAsync**: true **callback**( )

Answer 90

**Used** to **assert validation** on **schema fields Mongoose** ## Footnote **custom getter/setter available**

Answer 91

Create a **models folder** **extract logic** for **creating model** into **separate file** include **schema validation** logic in **separate file**

Answer 92

**Tradeoff** between **query peformance (embedded documents)** and **data consistency (references)** **References aka normalization** **Consistent data** but requires **additional query** for **getting the reference** **Embedded Documents (denormalization)** Single query to get both documents queries must run as fast as possible? use embedded docs

Answer 93

Embed **only half (parts)** of **another document** (**not full document**)

Answer 94

{**type**: mongoose.Schema. Types.ObjectId, **ref:** Author} **References** aka **normalization** **Consistent data** but **requires additional query** for **getting the reference**

Answer 95

.**populate** ('**property**') **query performance** is **reduced** by **having a second query** to get **reference object**

Answer 96

set **property** to a **schema** ## Footnote **subdocuments are same as reguar documents** **but can only be saved in context of parent**

Answer 97

don't reuse the **schema created** in **original model files** **documentID** will be **there** can **query database** for **full info** if **needed in the future** **Why?** **subdocuent could have 50 properties, we don't want to embed them all**

Answer 98

Using **Two Phase Commit** Fawn **3rd party library** does **it for us!**

Answer 99

**Virtually**, **yes** if more than **16 million documents** are **being updated** at same time **(in same process, on same machine)**, \_id: will become same, rare chance **\_id:** generated by **driver**, **not MongoDb** **Why?** **Don't** have to **wait for MongoDB** to **create a unique identify** **MongoDB driver** can create a **unique identifier** **mongoose** talks to **mongoDB driver** to **generate a unique ID**

Answer 100

generate **object ID in memory**, not **MongoDB** **ID generation by MongoDB driver, indpendent of MongoDB** **Don't have** to **wait** for **MongoDB** to **create a unique identify** **MongoDB driver** can **create a unique identifier,** pass to **mongoDB** **mongoose** talks to **mongoDB driver** to generate **a unique ID** without MongoDB

Answer 101

**There** is an **npm plugin** for **validating objectIDs** ## Footnote **\>npm i joi-ObjectId**

Answer 102

**Data consistency** - references **(one copy of data)**, **slower reads** **Performance** - embedded **subdocuments** (multiple copies of documents, **data inconsistency)**, faster reads

Answer 103

**Nearly**, **all applications** **require** some **authentication / authorization** **Authentication:** **The process** of **identifying if user is who they claim to be** aka **logging in - send username, password to server** **Authorization:** **determining** if user has **right permission** to **perform operation** only **logged in users** can **perform operations** to **modify data** **not logged in**, can **only read from API endpoint**s only **admins can delete data (permissions)** **How?** Add two **new API endpoint**s **Register**: POST /api/users **Login**: **POST** /**api/logins** (creating new resource, login)

Answer 104

**Extremely powerful** optimized **version of underscore** **utility functions** for working with **strings, arrays, etc.**

Answer 105

**use loadash** **\_.pick**(**object, [paths]**)

Answer 106

**never** ever **store passwords as plain text**

Answer 107

cannot **decript applications hash** can **compile a list of popular passwords**, hash them look at **our database**, find **what our passwords are** **a salt** is an **arbitrary string** placed **before our password** **Why?** **Hash password will be different each time based on the salt**

Answer 108

**npm i bcrypt**

Answer 109

Send **JSON web token**

Answer 110

**On client** store long string **(JSON token)** send to server A **long string** that **identifies a user,** **stored on client** **functions** like a **drivers license** or **password** when **client logins** in, **server** generates **JSON web token** **next time**, client **must send JSON web token** for **future API calls** on client, store JSON web token to send for future API calls **Stored?** **Web application** - local storage on every browser (React, Angular) Mobile APP - similar options

Answer 111

**Stored** on **client**, sent to **server with each client request** **(Header)** **alg - algorithm** used to encode JSON token **(Payload**) **basic public** properties **about user**, **sent to server** with **client request** can **extract name, user\_id, permissions**, etc. without **additional query to database from JSON web token** **(Digital Signature)** **digital signature** created **based** on content of **JSON web token** + **private key** **(only on server)** **Hacker** cannot **modify payload** without **re-creating the digital signature** using the **private key (only on secured server)**

Answer 112

const **jwt** = .**require**('jsonwebtoken') jwt.**sign**( { payload } , 'privateKey')

Answer 113

$ **export vidly\_jwtPrivateKey=mySecureKey** **npm config package** **config package** - store **config settings** in **JSON files / environment variables** **Steps:** **install config (npm i config)** **create config file in project** **create default.json** **create custom-environment-variables.json** **replace secret in app with call to config.get ( )** **secret stored in environment variable - export vidly\_jwtPrivateKey=mySecureKey** **(default.json)** to **store template** for **config settings** **(custom-environment-variables.json)** **specify mapping** between **app settings** and **environmental variables** Ex. Store **jwtPrivate** key **using config**

Answer 114

Send **JSON webtoken** in **header** as **response to client** store **JSON web token** on **client** with **each request**, send **JSON web token**

Answer 115

**Create** a **middleware function** **re-use** in **route handlers** that **require permissions** **router (route, \*middleware, callback)** **\*executed before callback**

Answer 116

**On client side** **delete token from client** **Why?** We never store the **JSON web token** on **server** (in the client header) **DO NOT** store token's on **server in database** (unless hashed) **Why?** If hacker gets database access can steal tokens **Use HTTPS** when **sending token from client to server**

Answer 117

**middleware function**

Answer 118

**401 unauthorized** - not a valid JSON, try again **403 forbidden** - valid JSON, not accessible

Answer 119

add a method to the userSchema prototype

Answer 120

**Send** a friendly **error to client** **log** the exception **on the server** **How?** **using promises - catch() rejected promise** **using await/async - wrap in try/catch blocks** **Why?** In **real world, issues happen** **logging** the **issues to see** which **happen frequently** is important Ex. Maybe mongoDB drops off line, promise reject is handled and node doesn't stop (crash)

Answer 121

In future, **unhandled promises** will crash application Send a **friendly error to client** log the **exception on the server** How? using promises - catch() rejected promise using await/async - wrap in try/catch blocks

Answer 122

create a **middleware function (async) that serves as a template** **pass route handler to middleware (encapsulates route in try/catch)** **Why?** Make **code less noisy** don't have to **repeat try-catch logic** **Problem?** Makes **route handler signature** a **bit noisy** Soln? **npm module** use **express-async-errors** **monkey patches routers at run time (wraps route in try/catch)**

Answer 123

**remove** **asyncMiddleware function** ## Footnote **make routes cleaner** **Mosh's recommendation for handling express-async errors**

Answer 124

In every **enterprise application,** must log errors **Why?** Determine **where we can improve** our application **What?** npm Winston

Answer 125

A **storage device** for our **logs** **Can be:** **Console** - logging errors on the console **File** - logging errors in a file **HTTP** - calling endpoint for logging errors **MongoDB** - plugin for logging errors in Mongo **Loggly** - popular log analysis

Answer 126

**error** - most important **warn** - warning **info** - store information about application in log, not error **debug** - writing debug information **silly**

Answer 127

npm i **winston** npm i **winston-mongodb** **only catches errors that are part of request processing pipline** **constrained to errors within express**

Answer 128

**exceptions** not caught in **try/catch block** **outside of express (route handlers)** **process object** is an **event emiter** **process.on**('uncaughtException', **(ex)** =\> **{** winston.error **(ex.message, ex)**; **});** **ONLY WORKS** WITH **SYNCHRONOUS CODE**

Answer 129

**process**.**on**('unhandledRejection', (ex) =\> { **winston.error**(ex.message, ex); })

Answer 130

It **violates** **separation of concern** **not how enterprise applications are built** **index.js** should **only orchestrate**, details **in separate modules** Ex. details of routes / database separate **Soln?** Create folder mkdir startup **add routes.js (file)** - move routes to separate module

Answer 131

1. **What** is **automated testing**? **writing code** to **test the application code's functionality**, then running that **test code** in an **automated fashion** 2. **Does** it **replace** **manual testing**? 3. **Do** I **really need it**? 4. **How** **should I do it**? 5. **Should** I write **test code first (TDD)** or **app code first?** **6. What should I test in my application?**

Answer 132

**Source code consists:** **Production Code** - application APIs **Test Code** - unit tests, integration tests, end to end tests

Answer 133

**Lot's of steps!** Workflow is **slow (**takes minutes)! As **application grows**, manual **testing of every function** (bit/peice) **grows exponentially.** To **test a function** in **the** **application manually**: Launch app Login Navigate Fill out a form Submit it verify the result \*\*many steps, slow workflow, cannot test many functions

Answer 134

**Call functions** directly with **test code** eliminating **manual testing workflow** **automated tests** are **repeatable** and **scalable** **can re-run tests at every touch point:** everytime you **change app code** everytime you **check code into a repository** before you **deploy your app**

Answer 135

can **re-run tests** at **every touch point:** **everytime** you **change app code** **everytime** you **check code into a repository** before you **deploy your app**

Answer 136

**testing code** on a **frequent basis**, **faster** than **manually** **automated testing** allows us to **catch bugs** **before deployment** **Deploy applications with confidence from testing by reducing number of bugs that go into deployment** **Refactor code with confidence - retest behavior of application after refactoring** **write higher quality functions - functions that work with various inputs and edge cases**

Answer 137

**reduces** the **number of bugs** that **go into production** not bug free software, but improves quality test **app code functionality frequently** (**changes, modifications)** **Catch bugs** before **you deploy application** **allows confidence knowing features/functions have passed testing**

Answer 138

**Unit test** **test** a **unit of the code _without_ external dependencies** **Integration test** **tests** a **class or multiple classes** **_with_** **external dependencies** **End-to-End Test** drive an **application through its UI**

Answer 139

**Great** for **testing** **conditional statements** and **loops** **use** to **test methods** with **complex logic** and **calculations** test a **unit of the code** indepent of **_external_ dependencies.** **Cheap to write** **Fast to execute** **Can run hundreds in a few second** **Can verify each building block** **doesn't give confidence in reliability of application**

Answer 140

**Test** with **external dependencies** **(web service, database, message queue)** ## Footnote **Tests integration of application with external dependencies** **slower to execute (read/write to database)** **gives confidence to application**

Answer 141

a **test** that **takes a few units (classes)** and **tests their behavior as a whole** **Two classes** tested together **defined as an integration test vs. unit test** (even though not using external resources) **DO NOT DO:** **Recipe** for writing **fragile tests (tests that break)** as **implementation of classes** changes, **tests break** these **tests slow you down** if **you've failed** at **doing integration testing**, you **probably did it wrong**

Answer 142

Drive an **application through UI** **tools** for creating **end to end tests** (Selenium) gives developers the **greatest confidence** they're **very slow, brittle** Only **test happy paths,** leave **edge case tests** to **unit tests** Ex. **Selenium** - record interaction of user with application, play back to check if app returns correct results

Answer 143

1. **They're very slow** - requires launching application, login, navigate, submit form, inspect results 2. **They're brittle** - small changes to the UI can break these tests

Answer 144

Each **application** contains all **testing catagories**! **Ratio depends** on **each project** **Testing should include:** **Unit Tests** **most tests** in this catagory easy to write, **quick execution** gives **little confidence** **Integration Tests** a **bunch** to test **integration of application code** with **external dependencies** **gives greater** **confidence** benefits of **end-to-end testing** without user interface hassle **End to End Tests** **few** E2E tests only test happy paths **leave edge** cases to **unit tests**

Answer 145

**methods** with **complex logic** (conditional statements) or **calculations** Can **quickly test** all **execution pathways** **not needed for testing an application that simply reads/writes data to a database**

Answer 146

**Methods/applications** that **simply read/write** data to a **database**

Answer 147

**Focus** on **writing** **good, clean, unit tests** NOT the **tooling** **tooling comes** and goes! **A Testing** **framework includes:** **1. library** **utility functions** to **write tests** **2. Test running** a **command line tool** that **runs tests** and **returns results** **Popular testing frameworks:** **Jasmine** **first test framework, includes all testing needs** **Mocha** **most popular npm test framework** **BUT requires 3rd party modules to cover all tests (chai, sinon)** **requires different webpages for viewing documents** **libraries may develop indepently and become incompatible in future** **Jest** **npm i jest --save/dev** **wrapper around Jasmine + additional features** **Mosh's personal favorite** **developed by Facebook** **includes Jasmine + code coverage tool** **used to test React apps**

Answer 148

**Wrapper** around **Jasmine** **Developed** by **Facebook** for **testing React apps** **npm i jest --save/dev** **any file that ends with .js(x) treated like test file** **update package.json "test": "jest"**

Answer 149

**moduleName.test.js** **moduleName.spec.js**

Answer 150

**cover all execution paths** **cover logic thoroughly** **Basic Guidelines:** **number** of **unit tests \>=** number of **execution paths** **Ex**. if **number** is **positive**, if **number** if **negative**, return 0

Answer 151

**verify** if a **result is correct** by **comparing to another function** (matcher) **Matchers for:** **numbers** toBeLessThanOrEqual ( ) toBe ( ) toEqual ( ) toBeCloseTo ( ) **strings**

Answer 152

**Use** jest **error messages** for **testing / debugging** ## Footnote **sometimes its a problem in production code** **sometimes its a problem in test code**

Answer 153

**organize tests** so they are **clean and mantainable** **tests** are **first class citizens** in **source code** **tests** are **as important** as **production code** **always group related tests inside describe ( )** **-a function in jest for grouping related tests** **-clean up code by removing *test* keyword w/ *it* keyword** **DO NOT:** **write ugly, fat, unmaintable tests!**

Answer 154

**refactor** - **change implementation** without **changing behavior** **refactor** a **method, re-run** **test to ensure nothing is broken** **Ex.**

Answer 155

Test **shouldn't** be **too specific** or **too general** **How?** use a **regular expression** search for **certain patterns**, not **exact string matches** Ex. test a method that generates the title or body of an email as long as **name of person** in string, okay (reg expression)

Answer 156

**Guidelines:** check for **existance of element in array** (**irrespective of position**) Do **not look** for **exact location of an element** (as a test) Do **not look for** exact **array size** **Example:** result. **toBeDefined** - too general result. **toBeNull** - too general result**[0]**.**toBe('USD')** - too specific, change sorting algo and it breaks result.length.toBe(3) - too specific, breaks if add more elements

Answer 157

**expect(result).toMatchObject**

Answer 158

Do **not get** a **result from exception** must **pass** a **callback function**

Answer 159

**Tedious** to **continually restart tests** from **terminal after every change** have **jest monitor changes** and **re-run tests automatically** **during production, keep one monitor with test code running / other with production code** **jest -watch--all**

Answer 160

replace **real implementation** of a function (calling **external resource)** with a fake **"mock" implementation** ## Footnote **in test, redefine external call (using a function)** **override method on prototype with a new function (fake implementation)**

Answer 161

**Using flags** Ex. If **notifyCustomer** is called, **mail.send** will be **called**, our **flag will become true** **testing interaction of notifyCustomer object with mail object** **better approach?** **JEST mock functions**

Answer 162

**helper functions (dummy functions)** **can check arguments passed to functions** **can easily check if a function has been called** **used to replace interaction with outside dependencies** **during unit testing (isolated test)** **.toHaveBeenCalled()** **.toHaveBeenCalledWith() - test method args (numbers, booleans, not string)** **Ex. re-write mock functions using Jest mock functions**

Answer 163

use **unit tests** to test **functions with algorithms** that have **zero or minimum external dependencies** avoid creating **too many mocks** too **many mocks**? use **integration testing**

Answer 164

generateAuthToken (user model) no external resources **no mocking** simply **call function** and **verify result** unit testing better than **integration test** **Why?** Don't have to **call an HTTP end point,** **excercise entire application stack** to verify result

Answer 165

testing our application with external resources need a real database (populate with test data) send HTTP request to server (database) make an assertion (response or database) Ex. Look at DB and verify new data is available

Answer 166

Get **db** from config module

Answer 167

send **HTTP requests** like using postman

Answer 168

**supertest npm (module)** allows us to **call API endpoints** like we **did manually with postman** **Server best practice** load the server, close server each time **beforeEach ( )** - allows us to do something before each test (load server) **afterEach( )** - allows us to do something after (close server)

Answer 169

**Cannot use** expect(res.body).toMatchObject(genre); **Why?** object\_id **Soln?** Must use .toHaveProperty()

Answer 170

# Define **happy path** **then**, in **each test**, change **one parameter** that **clearly aligns** with **name of the test** **How?** **create a function for happy path (re-use)** **setup test environment with beforeEach ( )** **Ex.** authentication testing define happy path (post request to server) change token (empty, invalid, valid)

Answer 171

Must use a **unit test** **create mocks (req, res, next):** 1. **req = {heade**r: **jest.fn().mockReturnValue**(token)} 2. **res = { }** **3. next** = jest.fn(); Ex. test **auth middleware** create a **user document** (w/ id, admin props) **generateAuthToken** based off user document pass token to **auth** fn **w/ mocks** (res, next) compare **auth fn output** w/ **user document** (test if auth decodes JWT)

Answer 172

Shows us **how much** of **our code** How much of **code** is **covered by tests**? What **scenarios have you not tested**? Use **Jest** to see how **much code has been covered** **Package.Json**: jest --watchAll --verbose --coverage

Answer 173

What are scenarios that haven't been tested? How much of code is covered by tests? Why? **Unit and Integration Testing** allow us to have **greater confidence** when **deploying our applications** **Test Frameworks** allow us to **write tests** that **verify behavior** before **deploying our applications** This **allows** us to **deploy** reliable products with **less bugs** **Where?** coverage folder index.html file Launch with live server

Answer 174

Tells us **where we are low** on **testing** (more tests needed) Ex. **Admin.js** needs more testing **% covered** not explicit coverage, % of code in file has been excercised by one or more tests

Answer 175

**Click** on the **file name** **highlighted red** is **not covered by tests** **Ex. genres.js - GET /:id** if invalid objectID, validateObjectId returns 404 BUT if valid objectID, **no test** for "genre not found" SOLN add test

Answer 176

An **approach to writing software** **Development** is **driven by tests:** **Write tests first, production code second** **Foundation** of **test driven development**: **Start,** by writing a **failing test** (no application code) **Next**, write **simplest application code** to **make it pass** (pass test) **Finally**, refactor code if necessary **Lastly,** repeat until feature is built Why? Don't have to change code or re-work code to test it **Source code is testable immediately** Deploy with confidence **Every line of production code is covered by tests** Simplier solutions **reduce over engineering complexity** write simplest code to make tests pass

Answer 177

**Don't have to change code or re-work code to test it** Source code is testable immediately **Deploy with confidence** Every line of production code is covered by tests **Simplier solutions** reduce over engineering complexity write simplest code to make tests pass

Answer 178

**How** do we **send a request** to our **server** to **return a movie**? Rental **model has properties.**.. customer movie date out (undefined) date returned (undefined) rental fee (undefined) When customer returns movie, we set return date and calculate payment on server **Approach?** Cannot update rental document (don't want client to set rental fee, our date out) create a **new endpoint for returning a movie** '/api/returns' send return request (add customerId and movieID) will look up rental, set return date / calculate rental

Answer 179

Write **test first** **by default**, will **fail if no production router exists** **write production router** until test passes

Answer 180

add **joi later** (during refactoring) ## Footnote **write clean tests**

Answer 181

# define **happy path** in **each case**, **change** **one parameter** that **would simulate an edge case**

Answer 182

**Test development:** **change one variable** **execute happy path** **analyze results** **Feature development:** **simplest implementation** **refactor later**

Answer 183

Add our **auth middleware now** replace **res.status(401).send('Unauthorized")** add **middleware (refactor)**

Answer 184

verify a property was set and saved in db

Answer 185

**Beauty of TDD (test driven development)** **100% of router** is **covered by tests** **Can refactor** and **re-run tests** **1. Add Joi -** refactor to validate request using joi

Answer 186

**create lookup** as a **static method** (available on Rental class) in the **rental model** Ex. **Static**: Rental.lookup() **instance**: new User().generateAuthToken()

Answer 187

**Static** * **Ex.** Rental.lookup() * available on the class * not working with particular object **Instance:** * **Ex**. new User.generateAuthToken() * method is only available on object (instance of class) * workig on particular object, result depends on object

Answer 188

handler is **too busy calculating** what **should happen with state of rental object** **information expert principle** **logic** to **modify state** of **an object** should be **encapsulated with object** **Soln?** **encapsulate logic in rental object (calculating rental fee, return date)**

Answer 189

**404 not found** **resource** **requested** is **no longer available**

Answer 190

**403 forbidden** **server has rejected your request**

Answer 191

**Platform as a Service (PaaS)** **Heroku**, Google Cloud Platform, AWS, Azure **great option** if you **don't want to get involved** with **infrastructure** **if you don't want to worry about servers, load balancers, reverse proxies, restarting application on crash** **Docker** if you want to **deploy to your own web servers** can create **image of application** and **deploy to any computers you want**

Answer 192

**Install** a **few packages** **npm i helmet** **middleware package** to **protect app from well known vulnerabilities** **protects headers and client side attributes from attacks** **npm i compression** **compress HTTP response** we **send to client**

Answer 193

add to **package.json** "**scripts**": { "test": "jest --watchAll --verbose --coverage ", **"start": "node index.js"** }, **"engines" : {** **"node" : "12.18.2"** },

Answer 194

**\>** Heroku create **Two things**: creates a **git repository in Heroku** **connects** **git remote** to **local git respository** **When** we **push changes to our local git repository** **Heroku will automatically** **download changes to our application code** (in local repositry)

Answer 195

**Heroku create** **git push heroku master** pushes code from local git repo to heroku repo

Answer 196

**through** the **terminal** **through** the **dashboard**

Answer 197

heroku **config: set** vidly\_jwtPrivateKey=123 heroku config \*in heroku, all **dynos (servers)** share **environment variables**

Answer 198

store **db password in environment variable** heroku **config:set** vidly\_db=mongodb+srv://vidly:1234@vidly.lmsvf.mongodb.net/?retryWrites=true&w=majority