I have a "SuperClass" with "info" as an instance variable. "SuperClass" has function "printInfo()". "printInfo()" needs to access instance variable "info".
I want to create a "SubClass" which also has method "printInfo()". I want to call printInfo() of "SuperClass" from "printInfo()" of "SubClass".
SuperClass = function()
{
this.info = "I am superclass";
console.log("SuperClass:");
};
SuperClass.prototype.printInfo = function(that)
{
console.log("printing from superclass printInfo");
console.log(that.info);
};
SubClass = function(){};
SubClass.prototype = new SuperClass();
SubClass.prototype.printInfo = function()
{
console.log("calling superclass");
this.constructor.prototype.printInfo(this);
console.log("called superclass");
};
var sc = new SubClass();
sc.printInfo();
SuperClass.prototype.printInfo = function()
{
console.log("printing from superclass printInfo");
console.log(this.info);
};
You are messing with the SubClass
's prototype with the SuperClass
's object, in this line
SubClass.prototype = new SuperClass();
the child's prototype should depend on the Parent's prototype. So, you can inherit like this
SubClass.prototype = Object.create(SuperClass.prototype);
Also, it is quite normal to change the constructor to the actual function, like this
SubClass.prototype.constructor = SubClass;
To keep your implementation generic, you can use Object.getPrototypeOf
, to get the parent prototype in the inheritance chain and then invoke printInfo
, like this
SubClass.prototype.printInfo = function() {
Object.getPrototypeOf(SubClass.prototype).printInfo(this);
};
Since, info
is defined in the SubClass
yet, it will print undefined
. You might also want to call the parent't constructor, like this
var SubClass = function() {
SuperClass.call(this);
};
Note: You are creating global variables, by omitting var
keyword before SuperClass
and SubClass
.