Javascript p3

Question 1

What three things are on the start-line of an HTTP request message?

Answer 1

• • an HTTP method, that describes the action to be performed.
• • the request target, usually a URL, or the absolute path of the protocol, port, and domain are usually characterized by the request context.
• • the HTTP version, which defines the structure of the remaining message, acting as an indicator of the expected version to use for the response.

Question 2

What three things are on the start-line of an HTTP response message?

Answer 2

• • the protocol version, usually HTTP/1.1
• • the status code, indicating success or failure of the request
• • the status text, a brief informational textual description of the status code to help a human understand the HTTP msg

Question 3

What are HTTP headers?

Answer 3

• • similar to the head of an html doc, they hold specifics relevant to the data they head
• • they let the client and the server pass additional information with an HTTP request or response. An HTTP header consists of its case-insensitive name followed by a colon (:), then by its value.

Question 4

Where would you go if you wanted to learn more about a specific HTTP Header?

Answer 4

MDN Web Docs ! :D

Question 5

Is a body required for a valid HTTP request or response message?

Answer 5

– nope

Question 6

What does the new operator do?

Answer 6

• • it calls a constructor function to make a new object with properties based on values given as arguments
• • it’s an instance of the object

- uses constructor function to make new instance of object, vs 
var newObj = obj.create(ogObj);

Question 7

What property of JavaScript functions can store shared behavior for instances created with new?

Answer 7

• • the Function.prototype property
• -
• • x.prototype.prop = ‘value’;
• • object.getPrototypeOf(x).prop;

Question 8

What does the instanceof operator do?

Answer 8

– it checks if the object is a product of the given constructor function

• • objX instanceof ObjectXMaker;
• • returns true

tests to see if the prototype property of a constructor appears anywhere in the prototype chain of an object. returns boolean

Question 9

What is a “callback” function?

Answer 9

A callback function is a function passed into another function as an argument, which is then invoked inside the outer function to complete some kind of routine or action.

Question 10

Besides adding an event listener callback function to an element or the document, what is one way to delay the execution of a JavaScript function until some point in the future?

Answer 10

– .setTimeout(func, delay)

Question 11

How can you set up a function to be called repeatedly without using a loop?

Answer 11

• • .setInterval(func, delay);

- - clearInterval(intervalID)

Question 12

What is the default time delay if you omit the delay parameter from setTimeout() or setInterval()?

Answer 12

– 0, meaning execute immediately/next cycle

Question 13

What do setTimeout() and setInterval() return?

Answer 13

a numeric, non-zero value which identifies the timer created by the call to setInterval()

Question 14

What is AJAX?

Answer 14

• • AJAX is a technique in webdev which allows a page to request data from a server and load it without having to reload the entire page
• • selective reloading
• • uses JSON/HTML/XML
• • jQuery makes AJAX easier to use

Question 15

What does the AJAX acronym stand for?

Answer 15

– the term Ajax is now used to
refer to a group of technologies that offer asynchronous functionality in the browser

Question 16

Which object is built into the browser for making HTTP requests in JavaScript?

Answer 16

– XMLHttpRequest

Question 17

What event is fired by XMLHttpRequest objects when they are finished loading the data from the server?

Answer 17

• • load

- - progress, error, abort, timeout, etc

Question 18

An XMLHttpRequest object has an addEventListener() method just like DOM elements. How is it possible that they both share this functionality?

Answer 18

• • prototypes

- - inherits from eventTarget

Question 19

explain:

var $userList = document.querySelector(‘#user-list’);
var xhr = new XMLHttpRequest();
xhr.open(‘GET’, ‘https://jsonplaceholder.typicode.com/users’);
xhr.responseType = ‘json’;
xhr.addEventListener(‘load’, function () {
console.log(xhr.status);
console.log(xhr.response);
for (let i = 0; i < xhr.response.length; i++) {
const newItem = document.createElement(‘li’);
newItem.textContent = xhr.response[i].name;
$userList.appendChild(newItem);
}
});
xhr.send()

Answer 19

…