Adding to an object through a function

Question

I am currently trying to add to an object through a function.

My code is:

var ob = {};

function add(f, fun) {
    ob[f] = fun();
}

add('hi', function() {
    alert('hello')
})

ob.hi()

So this is suppose to change ob to:

var ob = {
     hi: function(){
      alert('hello')
     }
}

It does alert hello but just from the triggering of the add function (which I want to stop) and not from the ob.hi() function.

Thanks for any help. If you want you can also check the fiddle

James Allardice · Accepted Answer · 2012-07-13 08:01:54Z

2

You are executing the function and assigning its return value to the property. You need to assign a reference to the function to the property instead. Change your add function:

function add(f, fun) {
    ob[f] = fun; //No invoking parentheses!
}

Here's an updated fiddle.

If you look at the console in your original fiddle you get a hint of what's going wrong:

Uncaught TypeError: Property 'hi' of object #<Object> is not a function

answered Jul 13, 2012 at 8:01

James Allardice

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1 Comment

Shawn31313 Over a year ago

You helped big, since now I finally fixed an issue I had with the library im building

Denys Séguret · Accepted Answer · 2012-07-13 08:08:19Z

1

Add your function as a property of your object :

ob['hi'] = function() {
    alert('hello')
};

or

ob[funname] = fun;

if the function was defined elsewhere.

Don't write a add function just to set a property. Replacing a standard feature of the language by a custom setter isn't going to make the code more readable.

And don't forget that you can define classes in javascript :

function Rect(x,y,w,h){
    this.x = x;
    this.y = y;
    this.w = w;
    this.h = h;
}

Rect.prototype.contains = function(x, y) {
    return x>=this.x && x<=this.x+this.w && y>=this.y && y<=this.y+this.h;
};

All objects created as new Rect(0, 1, 2, 3) have the contains function.

edited Jul 13, 2012 at 8:08

answered Jul 13, 2012 at 8:02

Denys Séguret

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2 Comments

Shawn31313 Over a year ago

Thanks for the answer but I will need to set more than one property and I will want to do this with a function

Denys Séguret Over a year ago

Apart for homework, I don't see a reason to use a function to replace a standard feature of the language. If you're building a library, follow best practices.

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