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).

Message:

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

Error Type:

SyntaxError

Cause for Error: Somewhere in the code, There are regular expression flags that are not valid.

Example 1: This example has valid RegExp flags.

Javascript

let patt = /GeeksforGeeks/i;
let str = 'This is GeeksforGeeks';
console.log(str.match(patt));

Output:

GeeksForGeeks

Example 2: In this example, After the second slash ‘GFG’ is used as a flag that is invalid.

Javascript

let patt = /Geek/GFG;
let str = 'This is GeeksforGeeks';
console.log(str.match(patt));

Output(in console):

SyntaxError: Invalid regular expression flags