JavaScript: prototype property
In JavaScript, prototype is a property of functions which easily allows for object extension and inheritance.
var x = {};
x.prototype; // undefined
x = [];
x.prototype; // undefined
x = function(){};
x.prototype; // Object
To extend an object with prototype:
Array.prototype.add = function() {
var length = this.length;
var sum = 0;
for (var i = 0; i < length; i++) {
if (!isNaN(this[i])) {
sum += this[i];
}
}
return sum;
};
[2, 3, 5, 'ha ha ha ha', 10].add(); //20
The above serves as an example. Do not extend native objects lightly. This topic is discussed extensively at javascriptweblog.
To inherit from an object with prototype:
var Parent = function() {
this.name = 'parent';
this.getName = function() {
return this.name;
};
};
var Child = function() {
this.name = 'child';
};
Child.prototype = new Parent();
Child.prototype.constructor = Child;
var p = new Parent();
p.getName(); // 'parent'
var c = new Child();
c.getName(); // 'child'
Child.prototype.actChildish = function() {
// childish behavior
};
c.actChildish();
p.actChildish(); // error
Note that updating Child’s prototype to include actChildish updates the already instantiated object c and that p did not get actChildish added to its prototype.
