Author: Michal Szymanski
What Is a Regular Expression?
A regular expression is a sequence of characters that forms a search pattern.
When you search for data in a text, you can use this search pattern to describe what you are searching for.
A regular expression can be a single character, or a more complicated pattern.
Regular expressions can be used to perform all types of text search and text replace operations.
Syntax
/pattern/modifiers;
Example
var patt = /mdbootstrap/i;
Example explained:
/mdbootstrap/i is a regular expression.
mdbootstrap 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 search for a
match, and returns the position of the match.
The replace() method returns a modified string where the
pattern is replaced.
Using String search() With a String
The search() method searches a string for a specified value and returns the position of the
match:
var str = "Visit mdbootstrap!";
var n = str.search("mdbootstrap"); // Return 6
Using String search() With a Regular Expression
Use a regular expression to do a case-insensitive search for "MDBootstrap" in a string:
var str = "Visit our website mdbootstrap";
var n = str.search(/mdbootstrap/i); // Return 18
Using String replace() With a String
The replace() method replaces a specified value with another value in a string:
<button onclick="myFunction()">Try it</button>
<p id="example-1">Please visit Microsoft!</p>
<script>
function myFunction() {
var str = document.getElementById("example-1").innerHTML; // Get the string "Please visit Microsoft!"
var txt = str.replace("Microsoft", "MDBootstrap"); // Replace "Microsoft" with "MDBootstrap"
document.getElementById("example-1").innerHTML = txt; // Put replaced string into a paragraph with ID = "example-1"
}
</script>
Live preview
Please visit Microsoft!
Use String replace() With a Regular Expression
Use a case insensitive regular expression to replace Microsoft with MDBootstrap in a string:
<button onclick="myFunction2()">Try it</button>
<p id="example-2">Please visit Microsoft!</p>
<script>
function myFunction2() {
var str = document.getElementById("example-2").innerHTML; // Get the string "Please visit Microsoft!"
var txt = str.replace(/microsoft/i, "MDBootstrap"); // Replace "microsoft" (event if it's lowercase) with "MDBootstrap"
document.getElementById("example-2").innerHTML = txt; // Put replaced string into a paragraph with ID = "example-1"
}
</script>
Note: Regular expression arguments (instead of string arguments) can be used in the methods above. Regular expressions can make your search much more powerful (case insensitive for example).
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