Question

I want to create a series of objects that inherit or copy instance properties from a base object. This has led me to a decision about which pattern to use, and I wanted to ask your opinions about which method was “better”.

//APPLY:
// ---------------------------------------------------------
//base object template
var base = function(){
   this.x = { foo: 'bar'};
   this.do = function(){return this.x;}
}

//instance constructor
var instConstructor = function (a,b,c){
   base.apply(this);//coerces context on base
   this.aa = a;
   this.bb = b;
   this.cc = c;
}

instConstructor.prototype = new base();

var inst = function(a,b,c){
    return new instConstructor(a,b,c);
}

//CLONE   
// --------------------------------------------------------- 
function clone(obj) {
    if (null == obj || "object" != typeof obj) return obj;
    var copy = obj.constructor();
    for (var attr in obj) {
        if (obj.hasOwnProperty(attr)) copy[attr] = obj[attr];
    }
    return copy;
}    

var x = {foo: 'bar'};

function instC(a,b,c){
     this.aa = a;
     this.bb = b;
     this.cc = c;
     this.x = clone(x);
};

instC.prototype.do = function(){
    return this.x;
}

they both achieve the same thing, namely unique instance properties based on a common template – the question is which one is more “elegant”

Answer 1

OK, so i’ve given this some further thought – and the answer stems from the use case. Where clone is copying properties into a given scope, apply is changing the scope surrounding the property. The former is better for mixins, the latter for inheritance.