How to create new instance of parent class in javascript

Question

I have a class that inherits from another. Within the base class, I'm wondering if it is possible to create and return a new instance of the calling parent class.

Here's an example:

Base:

var util = require('util');

var ThingBase = function(options) {
}

ThingBase.prototype.mapper = function(data) {
  // do a bunch of stuff with data and then
  // return new instance of parent class
};

Parent:

var FooThing = function(options) {
  ThingBase.call(this, options);
};

util.inherits(FooThing, ThingBase);

FooThing.someMethod = function() {
  var data = 'some data';
  var newFooThing = this.mapper(data); // should return new FooThing instance
};

The reason why I wouldn't just create a new instance from someMethod is that I want mapper to do a bunch of stuff to the data before it returns an instance. The stuff it will need to do is the same for all classes that inherit from Base. I don't want to clutter up my classes with boilerplate to create a new instance of itself.

Is this possible? How might I go about achieving something like this?

How does util.inherits look like? You can save a reference to the parent constructor there if you need it. — elclanrs
– elclanrs, Commented Jan 30, 2014 at 1:56
I fear you confuse the terminology? Usually a Child class does inherit from a Parent class, or a Specific class does inherit from a Base class. I've never heard of a Parent inheriting from anything (unless you have 3 classes in the discussed hierarchy, then there might be a GrandParent). — Bergi
– Bergi, Commented Jan 30, 2014 at 2:11

Community · Accepted Answer · 2017-05-23 12:28:38Z

3

Assuming that FooThing.prototype.constructor == FooThing, you could use

ThingBase.prototype.mapper = function(data) {
  return new this.constructor(crunch(data));
};

All other solutions would "clutter up [your] classes with boilerplate [code]", yes, however they don't rely on a correctly set constructor property.

edited May 23, 2017 at 12:28

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answered Jan 30, 2014 at 2:07

Bergi

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1 Comment

doremi Over a year ago

This is exactly what I needed. I didn't know about the constructor prototype. Thanks for that. In my case, I do have a correctly set constructor property via util.inherits, so this works perfectly.

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