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JavaScript Regular Expression Creation (Live Playground)

Regular expressions are patterns that help us match, search, and manipulate strings. In JavaScript, there are two ways to create regular expressions: using RegExp constructor and using regular expression literals.

Creating Regular Expressions with RegExp Constructor

To create a regular expression using the RegExp constructor, you can use the RegExp keyword followed by the pattern and optional flags as arguments.

const regex1 = new RegExp('pattern', 'flags');

Here's an example of creating a regular expression to match the word "hello":

const helloRegex = new RegExp('hello', 'i');

The i flag makes the pattern case-insensitive, so it will match "hello", "Hello", or "HELLO".

Creating Regular Expressions with Literals

Another way to create a regular expression is by using regular expression literals. Enclose the pattern between forward slashes /, and add optional flags after the second slash.

const regex2 = /pattern/flags;

Here's the same "hello" example using a literal:

const helloRegex = /hello/i;

Both the RegExp constructor and literals create a RegExp object with the same functionality. However, literals are generally considered more concise and easier to read.

Common Flags

There are several flags you can use to modify the behavior of a regular expression:

  • g (global): Search for all matches in the string, not just the first one.
  • i (case-insensitive): Ignore case when matching.
  • m (multiline): Treat the string as multiple lines, allowing ^ and $ to match the start and end of each line.

You can combine flags like this:

const regex3 = /hello/gi;

In this example, the regular expression will match all occurrences of "hello" in a string, regardless of case.

Live Playground, Try it Yourself


In this tutorial, we learned how to create regular expressions in JavaScript using both the RegExp constructor and regular expression literals. We also covered some common flags that can modify the behavior of a regular expression, such as case sensitivity, global search, and multiline matching. Regular expressions are a powerful tool in JavaScript for pattern matching, searching, and manipulating strings. As you become more familiar with regular expressions, you'll find them to be an invaluable resource for handling text data and solving various programming problems.