Don't see this as useful, as long as you don't need to know what the number was you can easily coerce any number into decimal by using a arithmetic operator.

+0xF -> 15
+020 -> 16
+15.0 ->15

Replying to [comment:1 sindresorhus]:

Don't see this as useful, as long as you don't need to know what the number was you can easily coerce any number into decimal by using a arithmetic operator.

Presumably (i haven't looked at the code) jQuery tries to convert the value to a number, so it would make sense to me to simply return it, rather than returning yes/no. That's simply mocking the user ("i know what the value is and now you may attempt to guess it yourself"). In many use cases that will lead to the double-decoding of numbers (once from jQuery and then again from the client code). Why make the client pay that conversion cost when jQuery has already paid it?

I've been thinking along these lines too, and could definitely go for something like the following:

ifNumeric: function( obj, fallback ) {
    obj = +obj;
    return isFinite( obj ) ? obj : fallback;
},

// deprecate?
isNumeric: function( obj ) {
    return jQuery.ifNumeric( obj ) != null;
}

Code like ret = parseFloat( orig ); return jQuery.isNumeric( ret ) ? ret : orig; (from jQuery.fn.width/height) would be reduced to return jQuery.ifNumeric( orig, orig );

I can see the utility of ifNumeric and if we used it in a dozen places like that it would make sense to define it just for the byte savings alone, even if we didn't expose it. But we only have two uses of it, and one doesn't fit that pattern, so I think we might as well stay with what we've already (just) documented and let this be a plugin or external code.

As for the original ticket suggestion, an isNumeric return value that broke 0 would be a big one in my book. This is a very simple one-line utility function so it's not hard to just ignore isNumeric and implement one line with whatever semantics you want in your own code. For example, perhaps you really want isInteger because real numbers and exponentials aren't valid in a particular case.

What if we can get it along with a 3-byte reduction?

https://github.com/jquery/jquery/pull/684