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Introduction to Regular Expressions in JavaScript


What exactly is a regular expression, and how is it handled in JavaScript? These are the questions tackled by this five-part series. In this first part, we'll introduce the topic of regular expressions (often abbreviated RegExp), and delve into objects, patterns, and variables.

Author Info:
By: Chrysanthus Forcha
Rating: 5 stars5 stars5 stars5 stars5 stars / 2
July 08, 2009
TABLE OF CONTENTS:
  1. · Introduction to Regular Expressions in JavaScript
  2. · Simple Word Matching
  3. · Meaning of Pattern
  4. · Regular Expression Object
  5. · Simple Usage of the Literal Text Format and the Constructor Function
  6. · The Flags

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Introduction to Regular Expressions in JavaScript - Simple Usage of the Literal Text Format and the Constructor Function
(Page 5 of 6 )

Assigning them to Variables

In the following code, the regexp is assigned to a variable using the Literal Text Format.


<script type="text/javascript">

var availableString = "Hello World";


var re = /World/;

if (re.test(availableString))

alert('Matched')

else

alert('Not Matched')

</script>


In the following code, the regexp is assigned to a variable using the constructor function.


<script type="text/javascript">

var availableString = "Hello World";


var re = new RegExp("World");

if (re.test(availableString))

alert('Matched')

else

alert('Not Matched')

</script>


Using them Directly in Conditional and Looping Expressions

In the following code, the literal text format is used directly in the if-conditional expression.


<script type="text/javascript">

var availableString = "Hello World";

 

if ((/World/).test(availableString))

alert('Matched')

else

alert('Not Matched')

</script>


The brackets around the regexp keep it as an entity.

In the following code, the constructor function is used directly in the if-conditional expression:


<script type="text/javascript">

var availableString = "Hello World";

 

if ((new RegExp("World")).test(availableString))

alert('Matched')

else

alert('Not Matched')

</script>


The brackets around the regexp keep it as an entity.

I prefer to assign them to variables than to use them directly in conditional and looping expressions. I believe this makes my code more readable and easier to maintain.


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