JavaScript RegExp Syntax- Tutorial

JavaScript RegExp Syntax: Video Lesson

            This video lesson, titled “RegExp Definition and Modifiers,” discusses the JavaScript RegExp syntax. This video lesson is from our complete introductory JavaScript course, titled “Mastering Introductory JavaScript Made Easy v.1.0.”

JavaScript RegExp Syntax: Overview

            RegExp stands for regular expression. In JavaScript, it is an object that describes a pattern of characters. When searching in text you can use a regular expression to describe what you are looking for, be it a single character or a whole word. To search using RegExp you need to specify a pattern and a modifier to allow your expression to search properly. The JavaScript RegExp syntax can be expressed in two ways:

var patt=/pattern/modifiers;

OR

var patt=new RegExp (pattern,modifiers);

            The first JavaScript RegExp syntax option above creates a RegExp object literal that provides compilation of the regular expression when the script is loaded. You will find this will give better performance when you know the regular expression is going to remain constant.

            The second JavaScript RegExp syntax option above creates a RegExp object using a constructor function. This JavaScript RegExp syntax option compiles the regular expression in runtime. This means that if you know the regular expression will change or you do not know the pattern, due to user input, this is the preferred method for RegExp object creation.

JavaScript RegExp Syntax- Tutorial: A picture showing the uses of the two different RegExp syntaxes in JavaScript.

            There are three basic modifiers, or flags, for RegExp, they are i, g, m. The i modifier is used when you want to perform a case-insensitive search. Case-insensitive means search all words and ignoring the capitalization of letters. The g modifier is used when searching “globally” in your code. This means it continues to search for a match after the first match is made and returns all matches in your code. The g modifier will only search for the expression you enter and is case sensitive. If you enter the expression var patt1=/or/g;, it will return matches containing “or”. For example, the word “or” would be chosen and the word “selector” would be chosen, as it contains the pattern “or”. You can also combine the modifiers to perform a global, case-insensitive search by using gi.

            The m flag, or modifier, is called the multiline flag. It is used to match the beginning (^) or end ($) of each line, delimited by \n (new line character) or \r (carriage return character), not only the very beginning or end of the input string as a whole. The m modifier stops after the first match and is case sensitive. To perform a global, case insensitive search, combine m with the g and i modifiers.