Beginning JavaScript

4th Edition

Chapter 5

JavaScript—An Object-Based Language

Chapter 5 Objectives

What are JavaScript objects?

How do you create a JavaScript object?

What are some of the useful built-in JavaScript objects?

What are JavaScript objects?

A JavaScript object is a collection of properties and methods that are grouped together with a single name.

An object is used to gather together everything needed for a particular task.

How do you create a JavaScript object? var myArray = new Array();

- the new keyword tells JavaScript that you want to create a new object

- the Array() constructor function tells JavaScript what kind of object you want to create

- a reference to the new object is stored in a variable named myArray

Primitive Data

Primitive data, such as text and numbers, is the most basic data possible in JavaScript.

With primitive data, the variable holds the data’s actual value:

var myNumber = 23;

Reference Data

A variable assigned to an object holds a reference to the memory address where the data can be found, not the actual data itself.

var myArray = new Array(“Paul”, “Jeremy”, “Nick”);

Accessing an object’s properties

To access the value of a property of an object:

- name of the variable referencing the object- dot- name of the property

myArray.length

Calling an object’s methods

To call the methods of an object:

- name of the variable referencing the object- dot- name of the method

myArray.sort();

JavaScript Native Objects

String

Math

Array

Date

String Object

A String is just a series of individual characters.

Each character has a position, or index.

The first position or index is 0.

String Object

Properties and Methods:

- vast number of properties and methods

- most common and least complex are covered in this chapter

String Object

Property:

length – the number of characters in the string

var myName = new String(“Jeremy");document.write(myName.length);

String Object Method:

charCodeAt() – returns the Unicode character code for the character at a specific position in the string

var myName = new String("Paul");var firstChar = myName.charCodeAt(0);alert(firstChar);

String Object Method:

fromCharCodeAt() – converts Unicode character codes to characters to create a string

var myString;myString = String.fromCharCode(65,66,67);alert(myString);

String Object

Method:

indexOf() – finds the index position of a substring inside a string

var myString = "Paul";var found = myString.indexOf("a" );

String Object

Method:

lastIndexOf() – finds the index position of a substring inside a string

var myString = "Paul";var found = myString.lastIndexOf("u" );

String Object Methods:

substr() and substring()– both methods copy part of a string, but they differ in the parameters used

var myString = "JavaScript";var mySubString = myString.substring(0,4);

String Object Methods:

toLowerCase() and toUpperCase()– both methods return a string converted either to lowercase or to uppercase

var myString = "JAVASCRIPT";var myString = myString.toLowerCase();

Array Object

An array is an object that can contain more than one item of data at the same time

Array Object

Property:

length – the number of items in an array var myNumber = new Array(2,4);alert (myNumber.length);

Array Object Method:

concat() – concatenates two arrays var myNumber = new Array(2,4);var myNumberA = new Array(3,5);var concatArray = myNumber.concat(myNumberA);

Array Object Method:

slice() – copy part of an array var names = new Array("Paul","Sarah","Louise","Adam","Bob");var slicedArray = names.slice(1,3);

Array Object Method:

join() – convert an array to a string var names = new Array("Paul","Sarah","Louise","Adam","Bob");var nameList = names.join(,);

Array Object Method:

sort() – put array in ascending order var names = new Array("Paul","Sarah","Louise","Adam","Bob");names.sort();

Array Object Method:

reverse() – put array in descending order var names = new Array("Paul","Sarah","Louise","Adam","Bob");names.reverse();

Math Object

The Math object provides a number of useful mathematical functions and number manipulation methods.

Math Object

Property:

PI – the value of the mathematical constant PI (3.14159… and so on)

var myPi = Math.PI;alert (myPi);

Math Object

Method:

abs() – returns the absolute value of the number passed as a parameter

var myNumber = Math.abs(-2);alert (myNumber);

Math Object

Method:

ceil() – rounds up to the next largest number

var myNumber = Math.ceil(103.1);alert (myNumber);

Math Object

Method:

floor() – removes any numbers after a decimal point and then rounds down

var myNumber = Math.floor(103.1);alert (myNumber);

Math Object Method:

round() – rounds up if decimal part is 0.5 or greater, otherwise rounds down

var myNumber = Math.round(103.1);alert (myNumber);

Math Object

Summary of Rounding Methods:

Math Object Method:

random() – returns a random floating-point number in the range between 0 and 1

var myNumber = Math.random() * 7;alert (myNumber);

Math Object

Method:

pow() – raises a number to a specific power

var myNumber = Math.pow(2,4);alert (myNumber);

Date Object

The Date object handles everything to do with date and time in JavaScript.

Date Object

Creating a Date object:

var myDate = new Date();

Date Object

Getting Date Values:

Date Object

Setting Date Values:

Date Object Getting Time Values:

* getHours()

* getMinutes()

* getSeconds()

* getMilliseconds()

* toTimeString()

Date Object Setting Time Values:

* setHours()

* setMinutes()

* setSeconds()

* setMilliseconds()