CODEWITHSUNDEEP
javascript
TJR
TJR

Reputation: 3773

What does this do?

I found this. What does it do?

function G(a, b) {
  var c = function() { };
  c.prototype = b.prototype;
  a.T = b.prototype;
  a.prototype = new c;
}

Upvotes: 4

Views: 303

Answers (2)

Christian C. Salvadó
Christian C. Salvadó

Reputation: 827416

It looks similar to the Crockford's Object.create method, but this function is used to "setup" constructors.

It accepts two constructors as arguments, and it setups the prototype of the first one.

Let me rename the cryptic variable names:

function G(sub, super) {
  var F = function() { };
  F.prototype = super.prototype;
  sub.superLink = super.prototype;
  sub.prototype = new F();
}

function Super () {
  //...
}
Super.prototype.member1 = 'superMember1';

function Sub() {
  this.member2 = 'subMember2';
}

G(Sub, Super);

new Sub(); // Object { member2="subMember2",  member1="superMember1"}

Edit: The T property is simply used to know what is the "super" constructor of the sub one, I've seen this pattern on other places, like in the book Pro JavaScript Design Patterns (page 43), with some additions, to prevent the constructor property to point to the wrong object:

function extend(subClass, superClass) {
    var F = function() {};
    F.prototype = superClass.prototype;
    subClass.prototype = new F();
    subClass.prototype.constructor = subClass;

    subClass.superclass = superClass.prototype;
    if(superClass.prototype.constructor == Object.prototype.constructor) {
        superClass.prototype.constructor = superClass;
    }
}

See also:

Upvotes: 1

JasonMichael
JasonMichael

Reputation: 2581

it looks like it gives you the ability to pass in a function, make changes to it, and then pass it back - a.prototype is a new instantiated copy of it. There are examples on the net using this type of code for "getting" and "setting".

Upvotes: 0

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