Question

In his sitepoint article about javascript inheritance, Harry Fuecks explains a way of implementing inheritance as follows:

    function copyPrototype(descendant, parent) {
    var sConstructor = parent.toString();
    var aMatch = sConstructor.match( /\s*function (.*)\(/ );
    if ( aMatch != null ) { descendant.prototype[aMatch[1]] = parent; }
    for (var m in parent.prototype) {
        descendant.prototype[m] = parent.prototype[m];
    }
};

While I understand his code, one question comes to mind – why not remove the for loop and simply do this:

 function copyPrototype(descendant, parent) {
    var sConstructor = parent.toString();
    var aMatch = sConstructor.match( /\s*function (.*)\(/ );
    if ( aMatch != null ) { descendant.prototype[aMatch[1]] = parent; }
    descendant.prototype = parent.prototype;
};

Thanks.

Answer 1

Assigning the prototype of one function to another would only assign a reference to the original prototype; both would be sharing the same prototype object. Iterating through the prototype creates a shallow copy of all its members.