Javascript - error extending object

Question

My code is like following:

function Example(){}
Example.myMethod = function(){};
function SpecificExample(){}
SpecificExample.prototype = Object.create(Example.prototype);
SpecificExample.prototype.constructor = SpecificExample;

I want SpecificExample extends Example. Why this code doesn't work?

Example.myMethod = function(){}; is a function attached to your constructor, not a prototype method, use Example.prototype.myMethod = function(){}; — somethinghere
– somethinghere, Commented Apr 5, 2016 at 15:26

somethinghere · Accepted Answer · 2016-04-05 15:31:18Z

2

Example.myMethod is a function attached to the constructor function/object, but it is not part of its prototype. This could be called a static function (and in ES6 it is exactly that). To make them part of your prototype, add them to the prototype itself:

function Example(){}
Example.prototype.myMethod = function(){};
function SpecificExample(){}
SpecificExample.prototype = Object.create(Example.prototype);
// As @JaredSmith said, you shouldn't change the constructor, and why would you?
// function SpecificExample(){} IS your constructor. So...
// SpecificExample.prototype.constructor = SpecificExample;
// should simply be removed.

edited Apr 5, 2016 at 15:31

answered Apr 5, 2016 at 15:28

somethinghere

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6 Comments

somethinghere Over a year ago

@JaredSmith Yeah technically a lot of stuff is possible, but yeah, you're right, better be correct. Let me change that.

Joy Over a year ago

Thanks you a lot, I know it is like a static method (I need it), the problem was that I can't change the constructor. @JaredSmith there are something like performance problems?

Jared Smith Over a year ago

More like unexpected behavior problems. Put a line Object.prototype = null; at the top of your script file as an example of why not to mess with built in stuff...

somethinghere Over a year ago

@Joy Actually, quick question: are you trying to make a sort of inheritable static method? Because I don't get why you want to change the constructor (certainly not since you are changing it to the same function that already is your constructor)...

Jared Smith Over a year ago

Also why you'd want an inheritable static method, which would almost certainly be an xy problem...meta.stackexchange.com/questions/66377/what-is-the-xy-problem

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