Introduction to Regular Expressions in JavaScript

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.