JS Exam study 1

Question 1

How do you alert the user?

Answer 1

alert()

Question 2

How do you print to the console?

Answer 2

console.log()

Question 3

How do you prompt the user?

Answer 3

prompt()

Question 4

what is used to declare variables?

Answer 4

var

Question 5

Javascript is dynamically typed, what does that mean?

Answer 5

A variable can hold a value of any type

Question 6

Javascript is weakly typed, what does that mean?

Answer 6

JavaScript uses aggressive type conversion so that any expression can be evaluated, regardless of whether the types of the operands match.

Question 7

What is explicit type conversion and how does it work?

Answer 7

parseInt() returns the integer equivalent of its argument (or NaN)
parseFloat()returns the Float equivalent of its argument (or NaN)
isNaN() returns true if the argument cannot by converted to a numb

Question 8

What are arrays in javascript?

Answer 8

arrays are objects that can hold a mix of data types.

Question 9

How do you initialize arrays?

Answer 9

You initialize them using array literals in square brackets or using new Array()
var a = [];
var a = new Array();
var a = [34, "hi", true]

Question 10

How do you access elements in an array?

Answer 10

a[1] = 67;

alert(a[1]);

Question 11

How do you extend an array?

Answer 11

You can extend them simply by assigning to a new index

Question 12

What to elements that are not defined yet return?

Answer 12

the special value undefined

Question 13

What is the DOM and what does DOM stand for?

Answer 13

DOM stands for Document Object Model, and it is the browser’s internal representation of the page.

Question 14

How is the DOM constructed?

Answer 14

The DOM is constructed from the page source as the page is loaded. It consists of a “tree” structure of Node objects. Each Node object represents a single HTML element (paragraph, image, etc.). The DOM can be changed in a JavaScript program after it is constructed.

Question 15

How does JavaScript properly output data?

Answer 15

A javascript app rarely uses alert, prompt, or confirm, and console.log is for debugging. The “output” of a JavaScript app consists almost entirely of changes to the DOM.

Question 16

How do you retrieve a node?

Answer 16

var node = document.getElementById("element id goes here")
returns node with matching id or null

Question 17

How do you retrieve an array like structure of nodes?

Answer 17

var nodes= document.querySelectorAll(“css selector goes here”)

returns a an array-like structure of elements that match the selector

can use nodes.length for the size, use a for loop to access each element

for(var i=0; i

Question 18

How do you change the contents of the node?

Answer 18

use the innerHTML field to change the contents of the node
- node.innerHTML = “New Message”
▪replaces contents with plain text
- node.innerHTML = “<p>New <a>Message</a></p>”
▪replaces contents with new nodes
- node.innerHTML = “”
▪deletes contents

Question 19

How do you change the style of the node?

Answer 19

use the style field to change CSS properties
- node.style.color = “red”;
- node.style.backgroundColor = “rgb(128, 0, 128)”
▪ note that hyphenated properties are changed to camel case

Question 20

How do you add or change HTML attributes?

Answer 20

use other fields to change or add HTML attributes

• node.href = “http://www.google.ca”
• node.title = “here’s a popup”
• node.src = “images/newImage.jpg”
• Important Exception…
  
  • To change the class
    attribute you have to use
    node.className(not
    node.class)

Question 21

What is associative array notation?

Answer 21

JavaScript object fields can be accessed using the dot operator or square brackets

E.g.
- node.style.color = “red”
is the same as
- node.style[“color”] = redoThe square bracket notation is