How to check if the input string is a valid Regular expression?

Question

How do you check, in JavaScript, if a string is a proper regular expression that will compile?

For example, when you execute the following javascript, it produces an error.

var regex = new RegExp('abc ([a-z]+) ([a-z]+))'); // produces: // Uncaught SyntaxError: Invalid regular expression: /abc ([a-z]+) ([a-z]+))/: Unmatched ')' 

How does one determine if a string will be a valid regex or not?

Answer 1

Here is a little function that checks the validity of both types of regexes, strings or patterns:

function validateRegex(pattern) {     var parts = pattern.split('/'),         regex = pattern,         options = "";     if (parts.length > 1) {         regex = parts[1];         options = parts[2];     }     try {         new RegExp(regex, options);         return true;     }     catch(e) {         return false;     } } 

The user will be able to test both test and /test/g for example. Here is a working fiddle.

Answer 2

You can use try/catch and the RegExp constructor:

var isValid = true; try {     new RegExp("the_regex_to_test_goes_here"); } catch(e) {     isValid = false; }  if(!isValid) alert("Invalid regular expression");