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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!