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JavaScript RegExp Object

admin — Thu, 18 Feb 2010 03:38:47 +0000

RegExp, is short for regular expression.

What is RegExp?

A regular expression is an object that describes a pattern of characters.

When you search in a text, you can use a pattern to describe what you are searching for.

A simple pattern can be one single character.

A more complicated pattern can consist of more characters, and can be used for parsing, format checking, substitution and more.

Regular expressions are used to perform powerful pattern-matching and "search-and-replace" functions on text.

Syntax

var txt=new RegExp(pattern,modifiers);

or more simply:

var txt=/pattern/modifiers;

pattern specifies the pattern of an expression
modifiers specify if a search should be global, case-sensitive, etc.

RegExp Modifiers

Modifiers are used to perform case-insensitive and global searches.

The i modifier is used to perform case-insensitive matching.

The g modifier is used to perform a global match (find all matches rather than stopping after the first match).

Example 1

Do a case-insensitive search for "w3schools" in a string:

var str="Visit W3Schools";
var patt1=/w3schools/i;

The marked text below shows where the expression gets a match:

Visit W3Schools

Example 2

Do a global search for "is":

var str="Is this all there is?";
var patt1=/is/g;

The marked text below shows where the expression gets a match:

Is this all there is?

Example 3

Do a global, case-insensitive search for "is":

var str="Is this all there is?";
var patt1=/is/gi;

The marked text below shows where the expression gets a match:

Is this all there is?

test()

The test() method searches a string for a specified value, and returns true or false, depending on the result.

The following example searches a string for the character "e":

Example

var patt1=new RegExp("e");
document.write(patt1.test("The best things in life are free"));

Since there is an "e" in the string, the output of the code above will be:

true

exec()

The exec() method searches a string for a specified value, and returns the text of the found value. If no match is found, it returns null.

The following example searches a string for the character "e":

Example 1

var patt1=new RegExp("e");
document.write(patt1.exec("The best things in life are free"));

Since there is an "e" in the string, the output of the code above will be:

JavaScript Math Object

admin — Thu, 18 Feb 2010 03:37:07 +0000

The Math object allows you to perform mathematical tasks.

Math Object

The Math object allows you to perform mathematical tasks.

The Math object includes several mathematical constants and methods.

Syntax for using properties/methods of Math:

var pi_value=Math.PI;
var sqrt_value=Math.sqrt(16);

Note: Math is not a constructor. All properties and methods of Math can be called by using Math as an object without creating it.

Mathematical Constants

JavaScript provides eight mathematical constants that can be accessed from the Math object. These are: E, PI, square root of 2, square root of 1/2, natural log of 2, natural log of 10, base-2 log of E, and base-10 log of E.

You may reference these constants from your JavaScript like this:

Math.E
Math.PI
Math.SQRT2
Math.SQRT1_2
Math.LN2
Math.LN10
Math.LOG2E
Math.LOG10E

Mathematical Methods

In addition to the mathematical constants that can be accessed from the Math object there are also several methods available.

The following example uses the round() method of the Math object to round a number to the nearest integer:

document.write(Math.round(4.7));

The code above will result in the following output:

The following example uses the random() method of the Math object to return a random number between 0 and 1:

document.write(Math.random());

The code above can result in the following output:

document.write(Math.random())0.9673354658127411

The following example uses the floor() and random() methods of the Math object to return a random number between 0 and 10:

document.write(Math.floor(Math.random()*11));

The code above can result in the following output:

document.write(Math.floor(Math.random()*11))6

JavaScript Boolean Object

admin — Thu, 18 Feb 2010 03:35:16 +0000

The Boolean object is used to convert a non-Boolean value to a Boolean value (true or false).

Create a Boolean Object

The Boolean object represents two values: "true" or "false".

The following code creates a Boolean object called myBoolean:

var myBoolean=new Boolean();

Note: If the Boolean object has no initial value or if it is 0, -0, null, "", false, undefined, or NaN, the object is set to false. Otherwise it is true (even with the string "false")!

All the following lines of code create Boolean objects with an initial value of false:

var myBoolean=new Boolean();
var myBoolean=new Boolean(0);
var myBoolean=new Boolean(null);
var myBoolean=new Boolean("");
var myBoolean=new Boolean(false);
var myBoolean=new Boolean(NaN);

And all the following lines of code create Boolean objects with an initial value of true:

var myBoolean=new Boolean(true);
var myBoolean=new Boolean("true");
var myBoolean=new Boolean("false");
var myBoolean=new Boolean("Richard");

JavaScript Array Object

admin — Thu, 18 Feb 2010 03:33:56 +0000

The Array object is used to store multiple values in a single variable.

What is an Array?

An array is a special variable, which can hold more than one value, at a time.

If you have a list of items (a list of car names, for example), storing the cars in single variables could look like this:

cars1="Saab";
cars2="Volvo";
cars3="BMW";

However, what if you want to loop through the cars and find a specific one? And what if you had not 3 cars, but 300?

The best solution here is to use an array!

An array can hold all your variable values under a single name. And you can access the values by referring to the array name.

Each element in the array has its own ID so that it can be easily accessed.

Create an Array

An array can be defined in three ways.

The following code creates an Array object called myCars:

var myCars=new Array(); // regular array (add an optional integer
myCars[0]="Saab"; // argument to control array’s size)
myCars[1]="Volvo";
myCars[2]="BMW";

var myCars=new Array("Saab","Volvo","BMW"); // condensed array

var myCars=["Saab","Volvo","BMW"]; // literal array

Note: If you specify numbers or true/false values inside the array then the variable type will be Number or Boolean, instead of String.

Access an Array

You can refer to a particular element in an array by referring to the name of the array and the index number. The index number starts at 0.

The following code line:

document.write(myCars[0]);

will result in the following output:

Saab

Modify Values in an Array

To modify a value in an existing array, just add a new value to the array with a specified index number:

myCars[0]="Opel";

Now, the following code line:

document.write(myCars[0]);

will result in the following output:

Opel

JavaScript Date Object

admin — Thu, 18 Feb 2010 03:31:48 +0000

The Date object is used to work with dates and times.

Create a Date Object

The Date object is used to work with dates and times.

Date objects are created with the Date() constructor.

There are four ways of instantiating a date:

new Date() // current date and time
new Date(milliseconds) //milliseconds since 1970/01/01
new Date(dateString)
new Date(year, month, day, hours, minutes, seconds, milliseconds)

Most parameters above are optional. Not specifying, causes 0 to be passed in.

Once a Date object is created, a number of methods allow you to operate on it. Most methods allow you to get and set the year, month, day, hour, minute, second, and milliseconds of the object, using either local time or UTC (universal, or GMT) time.

All dates are calculated in milliseconds from 01 January, 1970 00:00:00 Universal Time (UTC) with a day containing 86,400,000 milliseconds.

Some examples of instantiating a date:

today = new Date()
d1 = new Date("October 13, 1975 11:13:00")
d2 = new Date(79,5,24)
d3 = new Date(79,5,24,11,33,0)

Set Dates

We can easily manipulate the date by using the methods available for the Date object.

In the example below we set a Date object to a specific date (14th January 2010):

var myDate=new Date();
myDate.setFullYear(2010,0,14);

And in the following example we set a Date object to be 5 days into the future:

var myDate=new Date();
myDate.setDate(myDate.getDate()+5);

Note: If adding five days to a date shifts the month or year, the changes are handled automatically by the Date object itself!

Compare Two Dates

The Date object is also used to compare two dates.

The following example compares today’s date with the 14th January 2010:

var myDate=new Date();
myDate.setFullYear(2010,0,14);
var today = new Date();

if (myDate>today)
{
alert("Today is before 14th January 2010");
}
else
{
alert("Today is after 14th January 2010");
}

JavaScript String Object

admin — Thu, 18 Feb 2010 03:30:29 +0000

The String object is used to manipulate a stored piece of text.

String object

The String object is used to manipulate a stored piece of text.

Examples of use:

The following example uses the length property of the String object to find the length of a string:

var txt="Hello world!";
document.write(txt.length);

The code above will result in the following output:

The following example uses the toUpperCase() method of the String object to convert a string to uppercase letters:

var txt="Hello world!";
document.write(txt.toUpperCase());

The code above will result in the following output:

HELLO WORLD!

JavaScript Objects Introduction

admin — Thu, 18 Feb 2010 03:28:44 +0000

JavaScript is an Object Oriented Programming (OOP) language.

An OOP language allows you to define your own objects and make your own variable types.

Object Oriented Programming

JavaScript is an Object Oriented Programming (OOP) language. An OOP language allows you to define your own objects and make your own variable types.

However, creating your own objects will be explained later, in the Advanced JavaScript section. We will start by looking at the built-in JavaScript objects, and how they are used. The next pages will explain each built-in JavaScript object in detail.

Note that an object is just a special kind of data. An object has properties and methods.

Properties

Properties are the values associated with an object.

In the following example we are using the length property of the String object to return the number of characters in a string:

The output of the code above will be:

Methods

Methods are the actions that can be performed on objects.

In the following example we are using the toUpperCase() method of the String object to display a text in uppercase letters:

The output of the code above will be:

HELLO WORLD!