JavaScript & regex : How do I check if the string is ASCII only?

I know I can validate against string with words ( 0-9 A-Z a-z and underscore ) by applying W in regex like this:

function isValid(str) { return /^\w+$/.test(str); }

But how do I check whether the string contains ASCII characters only? ( I think I'm close, but what did I miss? )

################### answer ###################

All you need to do it test that the characters are in the right character range.

function isASCII(str) {
    return /^[\x00-\x7F]*$/.test(str);
}

Or if you want to possibly use the extended ASCII character set:

function isASCII(str, extended) {
    return (extended ? /^[\x00-\xFF]*$/ : /^[\x00-\x7F]*$/).test(str);
}

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