dictionary

Defining properties on objects in JavaScript seems like a very simple task. Just write object.property = value and you're done. However sometimes you may wish to have a more fine-grained control on how your properties are defined. This includes:

1. Defining getter and setter properties.
2. Defining non-enumerable properties.
3. Defining non-deletable properties.
4. Defining constant properties.

You can define such properties on objects using the native Object.defineProperty or Object.defineProperties functions. However these functions force you to write a custom property descriptor for each property, which is unnecessarily verbose and error prone.

Using dictionary you can easily define custom properties on objects in JavaScript. Let's learn by example.

Defining Getters and Setters

You can define getters and setters on objects in JavaScript using the __defineGetter__ and __defineSetter__ methods. However dictionary provides a more succinct and powerful way to define getters and setters:

var x = 0;
var o = {};

o.define({
    get x() {
        return x;
    },
    set x(y) {
        x = y;
    }
});

console.log(x);
o.x = 0xFFFFFF;
console.log(x);

Defining Non-Enumerable Properties

You can make a property non-enumerable by adding an underscore to the beginning of the property name. The underscore will be removed before actually defining the property:

var o = {};

o.define({
    _x: 0
});

for (var p in o) if (o.hasOwnProperty(p)) console.log(p);

console.log(o.x);

Defining Non-Deletable Properties

You can make a property non-deletable by adding an underscore to the end of the property name. The underscore will be removed before actually defining the property:

var o = {};

o.define({
    x_: 0
});

console.log(delete o.x);

Defining Constant Properties

Constant property names may only consist of numbers (0 to 9), upper case alphabets (A to Z) and the underscore. They may not be getters or setters. The property name is converted to camelCase before defining the property:

var o = {};

o.define({
    CONST_NUM: 0
});

o.constNum = 0xFFFFFFFF;
console.log(o.constNum);

That's All Folks

If you wish to contribute to this library then fork it on GitHub and send me a pull request. If you wish to suggest a feature then send me an email.