Updated on Kisan Patel
Regular expressions are search patterns that can be used to find text that matches a given pattern.
RegExp can be both a literal and an object. To create a RegExp literal, you use the following syntax.
var re = /regular expression/;
Modifiers can be used to perform case-insensitive more global searches.
| Modifier | Description |
| i | Perform case-insensitive matching |
| g | Perform a global match (find all matches rather than stopping after the first match) |
| m | Perform multiline matching |
Brackets are used to find a range of characters.
| Expression | Description |
| [abc] | Find any of the characters between the brackets |
| [0-9] | Find any of the digits between the brackets |
| (x|y) | Find any of the alternatives separated with | |
Metacharacters are characters with a special meaning.
| Metacharacter | Description |
| \d | Find a digit |
| \s | Find a whitespace character |
| \b | Find a match at the beginning or at the end of a word |
| \uxxxx | Find the Unicode character specified by the hexadecimal number xxxx |
Quantifiers define quantities.
| Quantifier | Description |
| n+ | Matches any string that contains at least one n |
| n* | Matches any string that contains zero or more occurrences of n |
| n? | Matches any string that contains zero or one occurrences of n |
The regular expression pattern is contained between opening and closing forward slashes. Note that this pattern is not a string: you do not want to use single or double quotes around the pattern.
For Example, the following is a regular expression for a pattern that matches against a string that contains the word Kisan and the word Patel, in that order, and separated by one or more whitespace characters.
var re = /Kisan\s+Patel/;
The RegExp is a JavaScript object as well as a literal, so it can also be created using a constructor, as follows:
var re = new RegExp("Kisan\s+Patel");
var patt = /study/;
patt.test("The string contains study text!"); // return true. sentence contains "study" text.
Use a JavaScript regular expression to define a search pattern, and then apply the pattern against the string to be searched, using the RegExp test method.
Use the String match method and a regular expression to validate that a string is a Social Security number.
var ssn = document.getElementById("pattern").value;
var pattern = /^\d{3}-\d{2}-\d{4}$/;
if (ssn.match(pattern))
alert("OK");
else
alert("Not OK");