composition vs. delegation

gistfile1.js

// composition

var obj1 = {
	doSomething: function(myId) {
		console.log( "Something: " + myId() );
	}
};

var obj2 = {
	id: "obj2",
	obj1: obj1,
	myId: function() { return this.id; },
	doAnother: function() {
		obj1.doSomething( this.myId.bind(this) );
	}
};

obj2.doAnother(); // Something: obj2

gistfile2.js

// delegation

var obj1 = {
	doSomething: function() {
		console.log( "Something: " + this.myId() );
	}
};

var obj2 = {
	id: "obj2",
	myId: function() { return this.id; },
	doAnother: function() {
		this.doSomething();
	}
};

// link for delegation
obj2.__proto__ = obj1;
// NOTE per @ljharb: __proto__ is discouraged in favor of `Object.setPrototypeOf(..)`
//   Object.setPrototypeOf( obj2, obj1 );
// Also, could have created `obj2` with the link, like:
//   var obj2 = Object.create( obj1 );
// Downside is we lose the nicer object-literal syntax. :/

obj2.doAnother(); // Something: obj2

With shimmed ES6 hotness you could do this:

var obj2 = Object.assign(Object.create(obj1), {
    id: "obj2",
    myId: function() { return this.id; },
    doAnother: function() {
        this.doSomething();
    }
});

Update: See my standalone Object.assign shim for lots of awesome examples, like [source1, source2, sourceN].reduce(Object.assign, target);!