JavaScript inheritance: when constructor has arguments

Question

Using pure JavaScript to do inheritance, this is what I usually do:

function A() {} A.prototype.run = function () {};  function B() {} B.prototype = new A; B.prototype.constructor = B; 

Since there is no arguments to pass into the constructor, new A has nothing to complain about. Now, I haven't figured out a good way to do inheritance if the constructor has arguments to pass. For example,

function A(x, y) {} A.prototype.run = function () {};  function B(x, y) {} B.prototype = new A; B.prototype.constructor = B; 

I could pass some arbitrary values like:

B.prototype = new A(null, null); 

In some cases, I may need to validate x and y in the constructor of A. In some extreme cases, I need throw errors when checking x or y. Then, there is no way for B to inherit from A using new A.

Any suggestions?

Thanks!

Answer 1

Well, if you want to make B.prototype an object that inherits from A.prototype, without executing the A constructor, to avoid all possible side-effects, you could use a dummy constructor to do it, for example:

function tmp() {} tmp.prototype = A.prototype; B.prototype = new tmp(); B.prototype.constructor = B; 

You could create a function to encapsulate the logic of the creation of this new object, e.g.:

function inherit(o) {   function F() {}; // Dummy constructor   F.prototype = o;    return new F();  }  //... B.prototype = inherit(A.prototype); B.prototype.constructor = B; 

If you target modern browsers, you could use the ECMAScript 5 Object.create method for the same purpose, e.g.:

B.prototype = Object.create(A.prototype); B.prototype.constructor = B; //..