JavaScript regular expression to negate an exact string match

Question

Is there a way in HTML (JavaScript) to write a regular expression to negate an exact string match?

I would like to make sure an input is not equal to " foo ". Only " foo " must fail validation, but " fooo " must be allowed.

In other words, I'm looking for a negation of this regex:

<input pattern="^foo$" ...>

Answer 1

One possible way is combining start of string anchor ( ^ ) with negative lookahead that includes both the target string and end of string anchor ( $ ):

/^(?!foo$)/

Demo .

But pattern pattern is funny in that account - it has to match something in the string, that's why the original approach doesn't work. This does work, however:

<input pattern="(?!foo$).*">

Answer 2

你可以使用这个正则表达式：

\bfooo\b

Answer 3

If Javascript is allowed, why not just negate the result of the match?

if (!yourString.match(/^foo$/)) {
    ...
}