JavaScript Reference: Objects

Objects are containers than can be given variable names, and can contain many properties surrounded by curly brackets {}. Each of these properties appears in the format name: value where name is the name of the property (and is completely up to you) and value is a string or number.

var bulldogObject = { breed: "English Bulldog", weight: 45, color: "brindle", name: "Rex" }

The properties of an object can be accessed in two ways:

bulldogObject.weight			// returns 45
bulldogObject["weight"]		// returns 45
bulldogObject.color			// returns "brindle"
bulldogObject["color"]		// returns "brindle"

We can also create a method for our object, which is stored in its properties as a function definition.

// Add a method to the object called 'printInfo'
var bulldogObject = { breed: "English Bulldog", weight: 45, color: "brindle", name: "Rex", printInfo: function() {console.log("I am a "+this.breed+" name "+this.name)}}
bulldogObject.printInfo()

would result in

Global objects are 'predefined' in JavaScript. These objects have their own methods and properties, many of which are listed in detail on these pages. For instance, a String object has properties like 'length' and methods like 'trim()', and so any string you create is interpreted as a String object and inherits those properties.

Global Values

Value	Description
Infinity	Positive infinity
NaN	Not a number
undefined	Undefined variable or function has been called
null	Empty value without type

Global Functions

Function	Use	Example	Example Returns
eval()	Evaluate a JS expression and return as a string NOTE: AVOID THIS FUNCTION	eval(6+5)	'11'
isFinite()	Returns true if value is finite, false otherwise	isFinite(3.14)	true
isNaN()	Returns true if value is not a number, false otherwise	isNaN('hello')	false
parseFloat()	Parses string as a floating point number	parseFloat('3.14') parseFloat('hello')	3.14 NaN
parseInt()	Parses string as integer with optional base	parseInt(25,3) parseInt("Hello", 8)	2 NaN

Strings, Dates, and Numbers

Object	Description
String	Wrapper for working with text (see Strings section for more)
RegExp	Creates regular expression for string pattern matching (see Strings section for more)
Number	Wrapper for working with numbers (see Math and Numbers section for more)
Math	Built in object for mathematics (see Math and Numbers section for more)
Date	Objects based on moment in time, measured in number of milliseconds since 1 January, 1970 UTC.