SyntaxError: invalid regular expression flag "x"

The JavaScript exception "invalid regular expression flag" occurs when the flags, defined after the second slash in regular expression literal, are not one 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

What went wrong?

There are invalid regular expression flags in the code. In a regular expression literal, which consists of a pattern enclosed between slashes, the flags are defined after the second slash. They can also be defined in the constructor function of the RegExp object (second parameter). Regular expression flags can be used separately or together in any order, but there are only six of them in ECMAScript.

To include a flag with the regular expression, use this syntax:

var re = /pattern/flags;

or

var re = new RegExp('pattern', 'flags');

Examples

There are only six valid regular expression flags.

/foo/bar;

// SyntaxError: invalid regular expression flag "b"

Did you intend to create a regular expression? An expression containing two slashes is interpreted as a regular expression literal.

let obj = {
  url: /docs/Web
};

// SyntaxError: invalid regular expression flag "W"

Or did you mean to create a string instead? Add single or double quotes to create a string literal.

let obj = {
  url: '/docs/Web'
};

Valid regular expression flags

See the table above for the six valid regular expression flags that are allowed in JavaScript.

/foo/g;
/foo/gims;
/foo/uy;

See also

• Regular expressions
• XRegEx flags – regular expression library that provides four new flags (n, s, x, A)