JavaScript SyntaxError - Invalid regular expression flag "x"

This JavaScript exception invalid regular expression flag occurs if the flags, written after the second slash in RegExp literal, are not from either of (g, i, m, s, u, or y).

Error Message on console:

SyntaxError: Syntax error in regular expression (Edge) 
SyntaxError: invalid regular expression flag "x" (Firefox)
SyntaxError: Invalid regular expression flags (Chrome)

Error Type:

SyntaxError

Common Causes and Examples

Case 1: Using an Unsupported Flag

Error Cause:

Using a flag that is not supported by JavaScript's regular expression engine will result in a SyntaxError.

Example:

let regex = /hello/x;
console.log(regex);

Output:

SyntaxError: Invalid regular expression flag "x"

Resolution:

Ensure that only supported flags are used in regular expressions.

let regex = /hello/i; // Using 'i' for case-insensitive search as an example
console.log(regex);

/hello/i

Case 2: Typo in Flag

Error Cause:

A typographical error in the regular expression flags can lead to an invalid flag error.

Example:

let regex = /world/gmxi; // 'x' is not a valid flag in JavaScript
console.log(regex);

Output:

SyntaxError: Invalid regular expression flag "x"

Resolution:

Correct the typo by using only valid flags.

let regex = /world/gmi; // Corrected to use only valid flags 'g', 'm', and 'i'
console.log(regex);

/world/gim