variables & types
Learning Javascript foundations
John Hunter
5 July 2008
1

var message = 'Hello';
...we’ve declared a variable - identified as
message - and assigned it a value of ‘Hello’
2

variable
identifier value
message 'Hello' type of:
String
3

types
type examples
String ' Apples' \"42\"
Number 42 3.12 -9
Boolean true false
Object (?)
Array (?)
... ...
4

Array
doors 4
0 red
colours 1 green
2 blue
model ‘Mazda6’
3 yellow
Numbers, Booleans and Strings can be
considered primitive types
Arrays and Objects are reference types
5

Javascript is a loosely typed language:
a variable can contain any type of
value at any time.
6

var pie = 'Apple';
// contains a string
pie = 3.12;
// contains a number
pie = true;
// contains a boolean
pie = someOtherVariable;
// contains who knows
pie can hold any value type at any time
7

Javascript has a simple way to define
a value and its type in one:
literals
8

var message = 'Hello';
// string literal
var count = 26;
// number literal
var height = 102.23;
// number literal
var isFinished = false;
// boolean literal
this is a familiar way to create primitive values
9

var letters = ['a', 'b', 'c'];
// array literal
var ages = [26, 31, 23, 42];
// array literal
var point = {x: 232, y: 102};
// object literal
var bookmark = {
name:
'Google',
url:
'http://google.com/',
lastVisited:
'20080518',
};
// object literal
objects and arrays are easy to create
using literals
10

var letters = ['a', 'b', 'c'];
Array
0 a
letters
1 b
2 c
the letters variable contains a reference to
the array
11

var point = {x: 232, y: 102};
Object
x 232
point
y 102
the point variable contains a reference to
the object
12

var bookmark = {
name:
'Google',
url:
'http://google.com/',
lastVisited:
'20080518',
};
Object
name Google'
bookmark
url 'http://google.com/'
lastVisited 20080518'
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Object
name Google'
bookmark
url 'http://google.com/'
lastVisited 20080518'
// alternative creation using the Object constructor
var bookmark = new Object();
bookmark.name = 'Google';
bookmark.url = 'http://google.com/';
bookmark.lastVisited = '20080518';
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object literal: object constructor:
cleaner, easier ugly
var bookmark = new Object();
var bookmark = {
bookmark.name =
'Google';
name:
'Google',
bookmark.url =
'http://google.com/';
url:
'http://google.com/',
bookmark.lastVisited =
'20080518';
lastVisited:
'20080518',
};
15

Review
variables consist of an identifier and a value
values have a type (e.g. string, number)
values are primitive or reference types
dynamic - variables can change value and type
literals define both type and value in one
object literals make it easy to create objects
16

Thanks
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