JavaScript

Question 1

What is the effect of using document.write() in the HTML body?

Answer 1

It inserts text into the document at that point.

Question 2

What is the effect of using document.write() in a function?

Answer 2

In this case, document.write() is called after the document has loaded, and overwrites the entire document.

Question 3

V8

Answer 3

Chrome’s JavaScript engine, written by Google

Question 4

node.js: process

Answer 4

process takes the place of window in regular javascript, because node apps run on a server, not a browser window. Node allows you to write javascript in a console.

Question 5

node: setTimeout and setInterval

Answer 5

Allow you to asynchronously schedule events. You never sleep in node.js

Question 6

curl

Answer 6

library and command-line tool for fetching data using URLs over http, ftp, and many other protocols. Handles cookies, very powerful.

Question 7

meta

Answer 7

HTML tag for providing metadata in key/value pairs. name=/content= pair used to specify generic metadata such as search terms (keywords), author, or description. Keys charset, http-equiv, and scheme(depr) offer other functionality.

Question 8

http-equiv

Answer 8

Simulates an http header response with appropriate key/values. Key content-type specifies encoding (eg text/html), key refresh will reload a web page at intervals, key default-style will load CSS.

Question 9

Where does javascript go in an html doc?

Answer 9

In the header or else linked in from an external file.

Question 10

What do legal javascript variables start with?

Answer 10

$ _ or a letter. Numbers can follow.

Question 11

What are the data types in javascript?

Answer 11

Numbers, strings, booleans, and objects. (Arrays are objects).

Question 12

What is Duck Typing?

Answer 12

It is a form of dynamic typing. In duck typing, an object’s methods and properties, rather than inheritance, determine its semantics.

Question 13

How do you add a method to an existing object?

Answer 13

person[‘getBirthday’] = function() {
return ‘July 18th’;
};

Question 14

Are javascript types completely dynamic type-inferred?

Answer 14

Javascript types are dynamic. You can create a variable, assign a string, number, an object, then a different object. Run time errors will only be generated when you use the variable in a way that violates semantic rules for whatever its dynamic type happens to be.

Question 15

What is the difference between “string” and ‘string’?

Answer 15

Nothing. Both forms work, and you can use one form to avoid escaping the other form ala:
“This isn’t hard.”
‘This is “hard”.’

Question 16

What does javascript do if you use a variable which has not been previously declared?

Answer 16

Error. Stops execution.

Question 17

How are javascript variables scoped?

Answer 17

Javascript variables are scoped to function, not block. Any extra ‘var’ declarations have no effect, where in other languages they may give you a new data store (such as declaring a variable in a loop).

Question 18

What is the associativity of +?

Answer 18

Left-associative. This matters, for example, when your are stringing together strings and numbers. “3”+4+9 will result in 349, NOT 313 (4+9=13).

Question 19

CSS: What is .foo { } ?

Answer 19

class selector. Targets all elements with class=’foo’

Question 20

CSS: What is #foo { } ?

Answer 20

id selector. Targets all elements with id=’foo’. According to spec, there should be only one.

Question 21

CSS: What is foo { } ?

Answer 21

element selector. Targets all HTML elements of type .

Question 22

CSS: What is foo.goo { } ?

Answer 22

element by class selector. Targets all HTML elements of with class=’goo’.

Question 23

How do you fetch an array of all elements by type?

Answer 23

getElementsByType(‘TAGTYPE’) returns an array

Question 24

Under the W3C HTML DOM standard, what are five categories of nodes?

Answer 24

• Document node (entire file)
• Element node
• Text node (text inside elements)
• Attribute node
• Comment node

Question 25

Which common HTML form element attribute indicates a function to be called when the element looses focus?

Answer 25

onBlur=”function()”

Question 26

Which object contains information about the browser?

Answer 26

navigator

Question 27

Which object and attribute gives you the browser?

Answer 27

navigator.appName

Question 28

What is the difference between null and undefined?

Answer 28

undefined is a type and is assigned to variables that have been declared but not assigned (although it can be assigned literally). null is an object.

Question 29

What is the alternative to foo.bar if bar is not a string literal and a legal javascript name?

Answer 29

foo[“bar”]

Question 30

How are objects passed and handled?

Answer 30

By reference

Question 31

What is happens with ‘foo.bar = “Hello”’ when bar is not a property of foo?

Answer 31

foo is augmented with bar.

Question 32

What is a prototype?

Answer 32

An object linked to objects which provides properties that can be inherited.

Question 33

What are the conditional statements?

Answer 33

if and switch

Question 34

What are the looping statements?

Answer 34

for, while, and do

Question 35

What are the disruptive statements?

Answer 35

break, return, and throw

Question 36

What is label syntax for statements?

Answer 36

name : statement

Question 37

What values are false?

Answer 37

false, null, undefined, ‘’, 0, NaN

Question 38

What special properties do functions have?

Answer 38

constructor(code), this, arguments, outer context

Question 39

What kind of function is this?
var a = function (a,b) {
return a+b
}

Answer 39

anonymous

Question 40

What are the four ways to invoke a function?

Answer 40

function, method, constructor, and apply

Question 41

How is ‘this’ bound in a method?

Answer 41

‘this’ is bound to the object owning the method. It is bound late, at invocation time, which makes methods highly reusable.

Question 42

How is ‘this’ bound in a function?

Answer 42

‘this’ is bound to the global object. This means that inner functions in methods cannot see the object (workaround: var that = this).

Question 43

What type of inheritance does JavaScript use?

Answer 43

Prototypal Inheritance. Contrast with Classical-Inheritance. JS is class-free.

Question 44

What happens when a function is invoked with new?

Answer 44

A new object is created. The object gets a hidden link to that function’s prototype property, ‘this’ is bound to the new object, and the meaning of ‘return’ for that function is temporarily changed.

Question 45

What is a constructor?

Answer 45

By invocation, it is a function called with ‘new’. By declaration, it is simply a function intended to be used as a constructor. Because there are no restrictions on what can be called with ‘new’, it is important to maintain a convention of Capitalized Constructors.

Question 46

What does ‘apply’ do?

Answer 46

Invokes a function with specified bindings for ‘this’ and arguments.

Question 47

What is returned from a constructor invocation?

Answer 47

If the return statement specifies an object, that object is returned. Otherwise, ‘this’ is returned.

Question 48

How can you make a method available to all objects?

Answer 48

Define the method on Object.prototype

Question 49

How do we augment all objects so that foo.method is supported for any object foo?

Answer 49

Add the method to Object.prototype ala Object.prototype.method = function(){}. You can do the same with functions, arrays, regular expressions, strings, numbers, and booleans.