Checking Object Types

JavaScript's "instanceof" operator checks an object for class information. But there are nuances that make it difficult in practice. For example, a DOM NodeList can be accessed like an array with [] subscripts, but "instanceof Array" applied to a NodeList returns false nonetheless. These Dojo base functions shield those nasty details from you.

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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"

            "http://www.w3.org/TR/html4/strict.dtd">

<html>

<head>

<title>Type Checking Demo</title>

        <script type="text/javascript" 

                    src="http://o.aolcdn.com/dojo/1.0.0/dojo/dojo.xd.js"></script>

        <script type="text/javascript">

            //

            dojo.addOnLoad(function() {

                var allScripts = dojo.query("script");

                var iceCreamObject = { flavor: "vanilla", scoops: 2};

                    // NodeLists are like arrays

                    console.debug(dojo.isArray(allScripts));  // True

                    // An arbitrary object.  Arrays are objects too.

                    console.debug(dojo.isObject(iceCreamObject));  // True

                    console.debug(dojo.isObject(allScripts));  // True

                    console.debug(dojo.isFunction(dojo.query)); // True

                    console.debug(dojo.isFunction(dojo)); // False

                    //  This next example hurts my head!

                    console.debug(dojo.isFunction(dojo.isFunction));  // True, but weird

                    // This is a common idiom for doing "nullable" arguments in the Dojo source code.

                    // Here, you can pass either myFn(var, function, var) or myFn(var, var);

                    var myFn = function() {

                       if (dojo.isFunction(arguments[1])) {

                          return arguments[1](arguments[0], arguments[2]);

                       } else {

                          return arguments[0]+arguments[1];

                       }

                    }

                    console.debug(myFn(1,2));  // 3

                    console.debug(myFn(1,Math.max,2));  // 2 = Math.max(1,2);

        });         

    </script>

</head>

</html>