Details on overriding prototype methods in JavaScript instance objects

In JavaScript , we can usually simply define a class like the following code:

var sample = function() {
    // constructor code here 
}

sample.prototype.func1 = function() {
    // func1 code here
}

sample.prototype.func2 = function() {
    // func2 code here
}

/* more sample prototype functions here... */

Then use the following code to instantiate and access the prototype method:

var sampleInstance = new sample();
sampleInstance.func1();
sampleInstance.func2();
// call more sample object prototype functions

But if we want to rewrite one of the prototype methods without destroying the original sample object, how to achieve it? The simplest way is to build another class to inherit sample , and then rewrite the base class method in the prototype method of the inherited class, as follows:

var subSample = function() {
    // constructor code here
}

// inherit from sample
subSample.prototype = new sample();
subSample.prototype.fun1 = function() {
    // overwrite the sample's func1
}

However, if you do not build an inherited class and want to rewrite the prototype method, you can directly use the following code:

var sampleInstance = new sample();
sampleInstance.func1 = function() {
    sample.prototype.fun1.call(this); // call sample's func1
    // sampleInstance.func1 code here
}

We redefined the func1 method of sample instance object, accessed its prototype method func1 , and then added some additional code to it. In this way, we extend the prototype method of sample without creating a derived class or destroying the prototype method of sample .

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