CODEWITHSUNDEEP
javascript
tjati
tjati

Reputation: 6079

Can access an attribute of my object but not a function

I have to figure out, how to develop oop-javascript the right way. I read a lot about prototypes but the internet explained to me, I need it only, if I create an object a lot of times. But my SuperInterface exists only once. So I created it as an object:

var SuperInterface = {
    superaction: function () {
        alert(1);
    },
    actions: [{
        title: 'This is great',
        do_this: this.superaction
    }],
    init: function () {
        console.log(this.actions[0].title);
        this.actions[0].do_this();
    }
};
SuperInterface.init();

Running init() puts the title successfully to the console. But the alert is never called. I do not understand, why not? What should I change?

Upvotes: 3

Views: 58

Answers (3)

Pointy
Pointy

Reputation: 413737

The value of this in the middle of that object initializer is not a reference to the object that is "under construction". There is no way to get such a reference during initialization since the object doesn't yet exist, and nor would you reference it with this. So you really can't initialize a property like that. You can however split it out into a separate statement:

var SuperInterface = {
    superaction: function () {
        alert(1);
    },
    actions: [{
        title: 'This is great',
        do_this: null;
    }],
    init: function () {
        console.log(this.actions[0].title);
        this.actions[0].do_this();
    }
};
SuperInterface.actions[0].do_this = SuperInterface.superaction;

Upvotes: 6

Vidul
Vidul

Reputation: 10538

var SuperInterface = {
    superaction: function () {
        alert(1);
    },
    actions: [{
        title: 'This is great',
        do_this: function() {
          return SuperInterface.superaction();
        }
    }],
    init: function () {
        console.log(this.actions[0].title);
        this.actions[0].do_this();
    }
};
SuperInterface.init();

this in your case refers to the literal object inside the array actions - it does not contain the method superaction.

Upvotes: 0

Kiba
Kiba

Reputation: 10827

If you debug this code, you will find SuperInterface.actions[0].do_this is undefined The reason is quite obvious. At the time of evaluation of code. 

  actions: [{
        title: 'This is great',
        do_this: this.superaction
    }]

this.superaction, here this points to the window object.

and in this window object superaction does'nt exits..

To make this work eventually you need to 

var SuperInterface = {
    superaction: function () {
        alert(1);
    },
    actions: [{
        title: 'This is great',
        do_this: null
    }],
    init: function () {
        console.log(this.actions[0].title);
        this.actions[0].do_this();
    }
};
SuperInterface.actions[0].do_this = SuperInterface.superaction;
SuperInterface.init();

I hope you got the answer. Thanks

Upvotes: 2

Related Questions