How best to determine if an argument is not sent to the JavaScript function

Question

I have now seen 2 methods for determining if an argument has been passed to a JavaScript function. I\'m wondering if one method is better than the other or if one is just ba

Answer 1

Some times you may also want to check for type, specially if you are using the function as getter and setter. The following code is ES6 (will not run in EcmaScript 5 or older):

class PrivateTest {
    constructor(aNumber) {
        let _aNumber = aNumber;

        //Privileged setter/getter with access to private _number:
        this.aNumber = function(value) {
            if (value !== undefined && (typeof value === typeof _aNumber)) {
                _aNumber = value;
            }
            else {
                return _aNumber;
            }
        }
    }
}

Answer 2

If you are using jQuery, one option that is nice (especially for complicated situations) is to use jQuery's extend method.

function foo(options) {

    default_options = {
        timeout : 1000,
        callback : function(){},
        some_number : 50,
        some_text : "hello world"
    };

    options = $.extend({}, default_options, options);
}

If you call the function then like this:

foo({timeout : 500});

The options variable would then be:

{
    timeout : 500,
    callback : function(){},
    some_number : 50,
    some_text : "hello world"
};

Answer 3

In ES6 (ES2015) you can use Default parameters

function Test(arg1 = 'Hello', arg2 = 'World!'){
  alert(arg1 + ' ' +arg2);
}

Test('Hello', 'World!'); // Hello World!
Test('Hello'); // Hello World!
Test(); // Hello World!

Answer 4

Why not using the !! operator? This operator, placed before the variable, turn it to a boolean (if I've understood well), so !!undefined and !!null (and even !!NaN, which can be quite interesting) will return false.

Here is an exemple:

function foo(bar){
    console.log(!!bar);
}

foo("hey") //=> will log true

foo() //=> will log false

Answer 5

fnCalledFunction(Param1,Param2, window.YourOptionalParameter)

If above function is called from many places and you are sure first 2 parameters are passed from every where but not sure about 3rd parameter then you can use window.

window.param3 will handle if it is not defined from the caller method.

Answer 6

function example(arg) {
  var argumentID = '0'; //1,2,3,4...whatever
  if (argumentID in arguments === false) {
    console.log(`the argument with id ${argumentID} was not passed to the function`);
  }
}

Because arrays inherit from Object.prototype. Consider ⇑ to make the world better.