Javascript

Front 1

why might a simple javascript command to change the contents of an element not work if it is placed above the element?

Back 1

the script element gets evaluated before the element it's acting on is processed

Front 2

what happens if you reference an html element that doesn't exist in an external javascript file?

Back 2

the javascript won't run

Front 3

how do you declare a variable? Many in a single statement?

Back 3

var var_name;
var var_1, var_2, var_3;

Front 4

how do you get information about the browser?

Back 4

via the navigator object
e.g.
navigator.userAgent() returns the user-agent header which tells what browser/device is being used

Front 5

how do you create an object using the object literal approach

Back 5

var instance_name =
{member_1:value,
member_n:value,
method: function(){[function_body]}
} ;

methods are just members whose value is an anonymous functions

Front 6

what is json?

Back 6

a data format that has the following form

{name:value,...}
where value can possibly be an array of form
[element, ...]
and element may be a json object

Front 7

what does array_instance.pop() do?

Back 7

it's a mutable function that returns and removes the last element of an array

Front 8

how do you get the attributes of a javascript object?

Back 8

[object name].toSource()

Front 9

what is the role of javascript in user interface construction?

Back 9

controlling behavior

Front 10

how do you create a javascript array and assign it to a variable?

Back 10

var varname = [value1, value2, ...];

Front 11

how do you create a function and name it?

Back 11

var functionName = function (arg1, arg2, ...) {
body
};

Front 12

how is a conditional written in javascript?

Back 12

if ( condition){
thing to do
}
else{
other thing to do
}

Front 13

how does javascript interact with an html page?

Back 13

through the DOM

Front 14

what is the DOM?

Back 14

a tree of objects that mirrors the nested structure of elements in a web page

Front 15

how do you access an html element by its id in javascript?

Back 15

document.getElementById('elementid');

Front 16

how do you get an array of html elements by their tag name in javascript?

Back 16

document.getElementsByTagName('tag');

Front 17

how would you do something like the css selector #about p{} in order to get all the p elements in the #about element?

Back 17

document.getElementsById('about').getElementsByTagName('p');

Front 18

how do you get a reference to a node for an element that is the parent of a given element?

Back 18

givenElement.parentNode

Front 19

what properties are useful for walking down the DOM tree?

Back 19

.childNodes, .firstChild, .lastChild

Front 20

how do you access elements horizontally in the DOM tree?

Back 20

.nextSibling, .previousSibling

Front 21

what is an event in javascript?

Back 21

things that occur when actions happen on a page

Front 22

what are the most common events?

Back 22

click, mouseover, mouseout, mousedown, mouseup, blur, focus, load

Front 23

what is the blur event?

Back 23

when a form element is not in focus anymore

Front 24

how do you use events in javascript and the DOM?

Back 24

attach a listener functions for an event to an element/node

Front 25

how do you add a listener function to an element?

Back 25

element.addEventListener('event_name', 'do_something_function', false);

Front 26

how do you check for whether you should use a browser specific function?

Back 26

if(elementReference.questionableFunction){
elementReference.questionableFunction();
}

Front 27

how do you change the style of an element in javascript?

Back 27

elementReference.style.property = 'newValue';

Front 28

what is the syntax format for dash-separated CSS names in javascript?

Back 28

camelCase

Front 29

what does the this keyword do in javascript?

Back 29

it is a reference to the object that owns the function from which this is called

Front 30

what is a good way to separate behavior and presentation instead of using javascript to change element styles directly?

Back 30

use javascript to change the class names usually through a javascript library function for adding or removing class names

Front 31

how do you use javascript to prevent the default behavior of an element?

Back 31

attach a listener function to the element and have it call
this.preventDefault();