Check if a Javascript Function Exists or Is Defined


It’s always frustrating when you get an error trying to call a function that hasn’t been defined but there’s an easy way  to prevent this. To check if a Javascript function exists before calling it, try this:

if (typeof yourFunctionName == 'function') { yourFunctionName(); }


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  • Tommy

    Finally! I’ve been looking for way too long for just this easy a solution! Thank you very very much!!!!

  • Bob

    terrific, you are on 1st place in google for javascript check it function exists, thank you

  • Darin Reid

    Hey neighbor, imagine my surprise when I googled this tonight. See you at coffee!

    • jeffreifman

      HA! We should cowork :) Email me your email again … as I can’t seem to find it.

  • MattC

    very nice. Simple an to the point – just what I was looking for. :)

  • Neil Young

    Great stuff, worked a treat – thanks for this!

  • Lutz Zimmmermann

    Great stuff, thanks a million!

  • Ken

    Jason Bunting’s answer on Stackoverflow is probably the better way to do this.

  • Nicola


  • Rolly Schicker

    Sounds like y’all are real happy with the solution…now for us dummies….where do you enter(type) all that good stuff?

  • Nikola

    Man you have been a great help, thank you for this trick

  • ray

    great solution thx!

  • Mark Giblin

    Try this.

    isFunc = function(func){ return typeof window[func] === “function”;}

    much better.

    returns true or false, func is the string name

    var x = isFunc(“myFunc”);

    x will be true or false depending on if myFunc is real or not.

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