typeof for RegExp

javascript regex constructor instanceof typeof
tau picture tau · Dec 2, 2010 · Viewed 41.1k times · Source

Is there anyway to detect if a JavaScript object is a regex?

For example, I would like to do something like this:

var t = /^foo(bar)?$/i;
alert(typeof t); //I want this to return "regexp"

Is this possible?

Thanks!

EDIT: Thanks for all the answers. It seems I have two very good choices:

obj.constructor.name === "RegExp"

or

obj instanceof RegExp

Any major pros/cons to either method?

Thanks again!

Answer

Cleiton picture Cleiton · Dec 2, 2010

You can use instanceof operator:

var t = /^foo(bar)?$/i;
alert(t instanceof RegExp);//returns true

In fact, that is almost the same as:

var t = /^foo(bar)?$/i;
alert(t.constructor == RegExp);//returns true

Keep in mind that as RegExp is not a primitive data type, it is not possible to use typeof operator which could be the best option for this question.

But you can use this trick above or others like duck type checking, for example, checking if such object has any vital methods or properties, or by its internal class value (by using {}.toString.call(instaceOfMyObject)).

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