Question

I have this code

function test(){};

test.prototype.testMethod = function(){return 1;}

var t = new test();
t.testMethod();

now I need to override the method testMethod so that I can still call the base method in the override.
How can I do that using prototype ?

Answer 1

If you need to overwrite the base method for an individual instance, you can still refer to the one defined in the prototype:

function test(){};

test.prototype.testMethod = function() {console.log('testMethod in prototype');}

var t = new test();
t.testMethod = function () {
    console.log(this);
    console.log('testMethod override');
    test.prototype.testMethod();    
};
t.testMethod();

Try it: http://jsfiddle.net/aeBWS/

If you want to replace the prototype method itself, you have a couple of routes. The most simple one is to just chose a different name for your function. If that isn’t possible, then you could copy the old method to one with a new name (like _testMethod) and call it that way:

function test(){};

test.prototype.testMethod = function() {console.log('testMethod in prototype');}  

test.prototype._oldTestMethod = test.prototype.testMethod;

test.prototype.testMethod = function() {
    console.log('testMethod override');
    test.prototype._oldTestMethod ();    
};

var t = new test();
t.testMethod();

Try it: http://jsfiddle.net/x4txH/