Call javascript dynamic method in object

Question

If I create a Class with two method like following:

var Car = function() {}
Car.prototype = {
    run: function() {
        alert('run');
    },
    stop: function() {
        alert('stop');
    }
}

And when the DOM is ready will call test() method,
and this test() method will create a instance of Car and call the method of Car

$(document).ready(function() {
    test("run");
});
function test(method) {
    var instance = new Car();
    // call instance.run()
}

I know I have to use apply() method,
but I have tried lots of times and failed
So, how can I use apply() method in Object?

perhaps I don't understand the question, but what's wrong on calling instance.run() directly ? — Zathrus Writer
– Zathrus Writer, Commented Oct 3, 2012 at 10:12
Am I missing something here, or you can just do instance.run()? — Sergio Tulentsev
– Sergio Tulentsev, Commented Oct 3, 2012 at 10:13
Because I want to call different method by using test(method), sometimes I can call test("run"), sometime test("stop") — Azure Chen
– Azure Chen, Commented Oct 3, 2012 at 12:23

Felice Pollano · Accepted Answer · 2012-10-03 10:45:02Z

2

An object in javascript is an associative array, so you can use the [] operator to address by string any member of the object, functions as well.

function test(method) {
    var instance = new Car();
    instance[method]();
}

this will allow to call a function by name over the object Car.

See it working on JsFiddle.

The context inside the called method will properly point to the newly created Car instance without any additional effort, that I guess is what you want. Using apply or call is generally used when you need to change the default 'this' value to something else.

edited Oct 3, 2012 at 10:45

answered Oct 3, 2012 at 10:16

Felice Pollano

33.4k10 gold badges77 silver badges125 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

user182669 Over a year ago

Try not to use "this" and "new" in your JS code. The best way to master it.

Quentin · Accepted Answer · 2012-10-03 10:13:20Z

1

I know I have to use apply() method,

You don't. Uncomment the instance.run() code, call the test() method and it works.

demo: http://jsfiddle.net/JkAnb/

how can I use apply() method in Object

It depends on what you want to achieve. There is documentation at MDN.

answered Oct 3, 2012 at 10:13

Quentin

948k136 gold badges1.3k silver badges1.4k bronze badges

Comments

Pankaj Kumar · Accepted Answer · 2012-10-03 10:23:26Z

1

perhaps you want to call

instance.method()

call dynamically i.e. based on value passed run/stop. You can try this -

instance[method].call(instance)

or

instance[method].apply(instance)

where instance is passed as scope param which is scope of the function to be called (value of "this" inside function).

edited Oct 3, 2012 at 10:23

answered Oct 3, 2012 at 10:17

Pankaj Kumar

535 bronze badges

Comments

user182669 · Accepted Answer · 2012-10-03 11:32:44Z

Why do You need classes in an (object based) functional language? Your intent is bit unclear. What is the implied type of the argument 'method' in Your test function? I assume it is a method name. In any case code bellow might help.

/* prefer this class pattern */
var Car = (function () {
    "use strict";
    Car.prototype = {
        name : undefined ,
        run: function () {
            return name_ + "::  run";
        },
        stop: function () {
            return name_ + "::  stop";
        }
    };
    /* constructor */
    function Car(name) {
        name_ = name;
    }
    return Car;
})();
function printer(msg_) {
   document.body.innerHTML += msg_ + "<br/>";
}
function test(car_, method_name_1, method_name_2) {
       printer(car_[method_name_1]());
       printer(car_[method_name_2]());
}
test( new Car("BMW"), "run", "stop");
test( new Car("Lada"), "run", "stop")

Veli Gebrev · Accepted Answer · 2012-10-03 10:38:41Z

-2

in addition, you could also use the eval function:

var instance = new Car();
eval('instance.'+method+'();');

though Felice Pollano's way is far neater imo.

http://jsfiddle.net/VZdXb/

edited Oct 3, 2012 at 10:38

answered Oct 3, 2012 at 10:32

Veli Gebrev

2,5414 gold badges32 silver badges49 bronze badges

1 Comment

cheeze Over a year ago

Using eval for this case is not necessary, and thus presents a security risk unnecessarily.

Collectives™ on Stack Overflow

Call javascript dynamic method in object

5 Answers 5

1 Comment

Comments

Comments

Comments

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

1 Comment

Comments

Comments

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related