40-RegExp.md

Regular Expression

Regular Expressions (also known as regex or regexp) are a tool used in JavaScript to match and manipulate text patterns. They are essentially search patterns that describe a certain set of strings.

For example, you can use a regular expression to find all email addresses in a block of text, or to ensure that a password meets certain criteria (such as containing at least one uppercase letter and one number).

Here's an example of a simple regular expression in JavaScript that matches any string that contains the word "hello":

var regex = /hello/;

This regex can be used with the test() method to see if a particular string matches:

regex.test("hello world"); // true
regex.test("goodbye"); // false

Another common use of regular expressions is to replace certain parts of a string, like replacing all occurrences of a word or character with another value. This can be done using the replace() method:

var str = "Hello, World!";
var regex = /Hello/;

str = str.replace(regex, "Hi");

console.log(str); // "Hi, World!"