Understanding the superior method introduced by Crockford

Question

In the functional inheritance pattern, Crockford introduces a new superior method via:

Object.method(\'superior\', function (name) {
    var th         


        

Answer 1

"My question is Why don't just assign that.get_name to super_get_name?"

Because the way the get_name method has its this value set to the that object is by invoking it as:

that.get_name();

When a function is invoked as the method of an object, the object becomes the value of this in that invocation of the function.

If you had done this instead:

var super_get_name = that.get_name;

super_get_name();

Now you're invoking a detached function, so it doesn't know what its this value should be, and so it uses the default, which is usually the window object.

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I don't like the solution that crockford shows at all. Typically, in that situation, you'd simply make a new function right there instead of relying on extensions to Object.prototype to do it for you. (Extending Object.prototype is very ugly IMO.)

var coolcat = function (spec) {
    var that = cat(spec),
        _original_get_name = that.get_name,
        super_get_name = function() {
                             return _original_get_name.apply(that, arguments);
                         };

    that.get_name = function (n) {
        return 'like ' + super_get_name() + ' baby';
    };
    return that;
};

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Or in modern implementations, you'd use Function.prototype.bind to create a new function with its this value bound to whatever you provided as the first argument to .bind().

var coolcat = function (spec) {
    var that = cat(spec),
        super_get_name = that.get_name.bind(that);

    that.get_name = function (n) {
        return 'like ' + super_get_name() + ' baby';
    };
    return that;
};