jQuery: Check if Function Exists before Calling

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This post shows how to check if a function exists, before calling it. We will use both JavaScript as well as jQuery (JavaScript library) to do so.

Using JavaScript

In order to check if a function exists using plain JavaScript, use the following code:

The output is the following:

Using jQuery

jQuery contains the jQuery.isFunction() which finds out if the parameter passed to it is a function.

<script type="text/javascript">
    function calculateSum() {
    }  

    // using jQuery
    if ($.isFunction(window.calculateSum))
        calculateSum();
    else
        document.writeln('calculateSum does not exist');
</script>

Since calculateSum() exists, the method gets called.

Check plenty of similar jQuery/JavaScript tips here

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About The Author

Suprotim Agarwal, Developer Technologies MVP (Microsoft Most Valuable Professional) is the founder and contributor for DevCurry, DotNetCurry and SQLServerCurry. He is the Chief Editor of a Developer Magazine called DNC Magazine. He has also authored two Books - 51 Recipes using jQuery with ASP.NET Controls. and The Absolutely Awesome jQuery CookBook.

Follow him on twitter @suprotimagarwal.