Handling optional parameters in javascript

Question

I have a static javascript function that can take 1, 2 or 3 parameters:

function getData(id, parameters, callback) //parameters (associative array) and callb         


        

Answer 1

Er - that would imply that you are invoking your function with arguments which aren't in the proper order... which I would not recommend.

I would recommend instead feeding an object to your function like so:

function getData( props ) {
    props = props || {};
    props.params = props.params || {};
    props.id = props.id || 1;
    props.callback = props.callback || function(){};
    alert( props.callback )
};

getData( {
    id: 3,
    callback: function(){ alert('hi'); }
} );

Benefits:

• you don't have to account for argument order
• you don't have to do type checking
• it's easier to define default values because no type checking is necessary
• less headaches. imagine if you added a fourth argument, you'd have to update your type checking every single time, and what if the fourth or consecutive are also functions?

Drawbacks:

• time to refactor code

If you have no choice, you could use a function to detect whether an object is indeed a function ( see last example ).

Note: This is the proper way to detect a function:

function isFunction(obj) {
    return Object.prototype.toString.call(obj) === "[object Function]";
}

isFunction( function(){} )