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JavaScript Regular Expressions

A regular expression is defined as a sequence of characters that result in formation of a search pattern.

The search pattern can be used for text search and text replace operations.

What Is a Regular Expression?

A regular expression is defined as a sequence of characters that generates a search pattern.

When data is searched in a text, this search pattern is used to describe what you are searching for.

A regular expression can be a single character or a more complicated pattern.

Regular expressions perform all types of text search and text replace operations.

Syntax

/pattern/modifiers;

Example

/tutorial/i;

Example explained:

/tutorial;/i  is a regular expression.

A tutorial is a pattern (to be used in a search).

i  is a modifier (modifies the search to be case-insensitive).

Using String Methods

In JavaScript, regular expressions are often used with the two string methods: search() and replace().

The search() method uses an expression to find a match and returns the position of the match.

The replace() method is used to return a modified string where the pattern is replaced.

Using String search() With a String

The search() method is used to search a string for a defined value and returns the position of the match:

Example

<!DOCTYPE html>

<html>

<body>

<h2>JavaScript String Methods</h2>

<p>Search a string for “Webhostguru”, and display the position of the match:</p>

<p id=”demo”></p>

<script>

let text = “Visit Webhostguru!”;

let n = text.search(“Webhostguru”);

document.getElementById(“demo”).innerHTML = n;

</script>

</body>

</html>

Output

JavaScript String Methods

Search a string for "Webhostguru", and display the position of the match:

6

Using String replace() With a String

The replace() method is used to replaces a specified value with another value in a string.

Example

<!DOCTYPE html>

<html>

<body>

<h2>JavaScript String Methods</h2

<p>Replace “Microsoft” with “Webhostguru” in the paragraph below:</p>

<button onclick=”myFunction()”>Try it</button

<p id=”demo”>Please visit Microsoft!</p>

<script>

function myFunction() {

let text = document.getElementById(“demo”).innerHTML;

 document.getElementById(“demo”).innerHTML =

 text.replace(“Microsoft”,”Webhostguru”);

}

</script>

</body>

</html>

Output

JavaScript String Methods

Replace "Microsoft" with "Webhostguru" in the paragraph below:

Please visit Microsoft!

Use String replace() With a Regular Expression

Example

Using a case insensitive regular expression to replace Microsoft with tutorial in a string:

<!DOCTYPE html>

<html>

<body>

<h2>JavaScript String Methods</h2>

<p>Replace “Microsoft” with “Webhostguru” in the paragraph below:</p>

<button onclick=”myFunction()”>Try it</button>

<p id=”demo”>Please visit Microsoft!</p>

<script>

function myFunction() {

  let text = document.getElementById(“demo”).innerHTML;

 document.getElementById(“demo”).innerHTML =

  text.replace(/microsoft/i, “Webhostguru”);

}

</script>

</body>

</html>

Output

JavaScript String Methods

Replace "Microsoft" with "Webhostguru" in the paragraph below:

Please visit Microsoft!

Using test()

The test() method is a RegExp expression method.

It finds a string for a pattern, and returns true or false, depending on the result.

The following example searches a string for the character “e”:

Example

<!DOCTYPE html>

<html>

<body>

<h2>JavaScript Regular Expressions</h2>

<p>Search for an “e” in the next paragraph:</p>

<p id=”p01″>The best things in life are free!</p>

<p id=”demo”></p>

<script>

let text = document.getElementById(“p01”).innerHTML;

const pattern = /e/;

document.getElementById(“demo”).innerHTML = pattern.test(text);

</script>

</body>

</html>

Output

JavaScript Regular Expressions

Search for an "e" in the next paragraph:

The best things in life are free!

true

Using exec()

The exec() method is a RegExp expression method.

It finds a string for a definite pattern, and returns the found text as an object.

If no match is found, it returns an empty (null) object.

The following example searches a string for the character “e”:

Example

<!DOCTYPE html>

<html>

<body>

<h2>JavaScript Regular Expressions</h2>

<p id=”demo”></p>

<script>

const obj = /e/.exec(“The best things in life are free!”);

document.getElementById(“demo”).innerHTML =

“Found ” + obj[0] + ” in position ” + obj.index + ” in the text: ” + obj.input;

</script>

</body>

</html>

Output

JavaScript Regular Expressions

Found e in position 2 in the text: The best things in life are free!


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