How to Fix the ‘SyntaxError: invalid regular expression flag “x” ‘ Error in Our JavaScript App?

Sometimes, we may run into the ‘SyntaxError: invalid regular expression flag "x"’ when we’re developing JavaScript apps.

In this article, we’ll look at how to fix the ‘SyntaxError: invalid regular expression flag "x"’ when we’re developing JavaScript apps.

Fix the ‘SyntaxError: invalid regular expression flag "x"’ When Developing JavaScript Apps

To fix the ‘SyntaxError: invalid regular expression flag "x"’ when we’re developing JavaScript apps, we should make sure that we add flags to our JavaScript regex that’s accepted by the JavaScript engine.

On Edge, the error message for this error is SyntaxError: Syntax error in regular expression.

On Firefox, the error message for this error is SyntaxError: invalid regular expression flag "x".

And on Chrome, the error message for this error is SyntaxError: Invalid regular expression flags.

The general format for a JavaScript to declare a JavaScript regex is:

const re = /pattern/flags;

We can also use the RegExp constructor to declare a regex:

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

The following flags are valid JavaScript regex flags:

• g Global search.
• i Case-insensitive search.
• m Multi-line search.
• s Allow . to match newlines (added in ES2018)
• u Unicode; treat pattern as a sequence of Unicode code points
• y Perform a "sticky" search that matches starting at the current position in the target string.

Therefore, we shouldn’t write code like:

/foo/bar;

since bar isn’t a valid JavaScript regex flag.

Instead, we write:

/foo/g;

which has the g flag, which is a valid flag.

Conclusion

To fix the ‘SyntaxError: invalid regular expression flag "x"’ when we’re developing JavaScript apps, we should make sure that we add flags to our JavaScript regex that’s accepted by the JavaScript engine.

On Edge, the error message for this error is SyntaxError: Syntax error in regular expression.

On Firefox, the error message for this error is SyntaxError: invalid regular expression flag "x".

And on Chrome, the error message for this error is SyntaxError: Invalid regular expression flags.