Convert user input string into regular expression using JavaScript
Last Updated :
28 Apr, 2023
In this article, we will convert the user input string into a regular expression using JavaScript.To convert user input into a regular expression in JavaScript, you can use the RegExp constructor. The RegExp constructor takes a string as its argument and converts it into a regular expression object
Regular expressions (RegExp) are patterns used to match character combinations in strings. In JavaScript, regular expressions are also objects. There are two ways to construct a regular expression in JavaScript.
Using a regular expression literal, which consists of a pattern enclosed between slashes, as follows.
const reg = /ab+/;
Calling the constructor function of the RegExp object, as follows.
const reg = new RegExp('ab+', flag);
Using the constructor function provides run time compilation of the regular expression, hence we should use the second method here as the string is a dynamic input from the user. Both the above expressions correspond to the same RegExp.
Example 1: For the string, we will take “Geeks For Geeks'”.
Input : '^Ge'
Output: ["Ge"]
0: "Ge"
Input : '[A-z]+'
Output: (3) ["Geeks", "For", "Geeks"]
0: "Geeks"
1: "For"
2: "Geeks"
Javascript
const str = "Geeks for Geeks" ;
const regex = prompt( "Enter RegExp" );
const reg = new RegExp(regex, "g" );
const result = str.match(reg);
if (result) console.log(result);
else console.log( "Not Found" );
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Output:
Example 2: In this example, we will use the RegExp constructor.
Javascript
const userInput = prompt( "Enter a regular expression pattern:" );
const regex = new RegExp(userInput);
console.log(regex);
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Output:
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