Variable methods in Javascript objects

Question

I wand to check for the existence of a JavaScript method, when I have a variable with that method name inside it.

Using PHP I could do this:

$method = 'bar';
$object = new Foo;
if(method_exists($object, $method))
{
    //Foo->bar()
}

How can I do this in JavaScript? My first attempt failed:

var method = 'bar';
if(typeof(obj.method) != "undefined")
{
    obj.method();
}
else
{
    obj.default();
}

Answer 1

Check if the typeof the property is "function" , using method as the key into the obj object:

((typeof obj[method] === "function") ? obj[method] : obj.default)();

Answer 2

I typically just do if(obj.method) {...} but you could always use a try/catch:

try {
    obj.method();
} catch(e) {
    // obj or obj.method didn't exist, so let's try plan b
    obj.planB();
}

Answer 3

  (obj[method] || obj.default)();

would work too, if you want to one-line it.

Answer 4

['blah'] and .blah are equivalent in a Javascript Object, so you can call your method like

obj[method]();

Where method is a string containing the name of the method to call.

Answer 5

You should the object's method property to be typeof as function . Eg

 if (typeof(obj[method]) == "function") {
   obj[method]();
 }

Here is a JSFiddle explaining how to check for a function.