Creating object dynamically using Object.create()

Question

I have a scenario, where I need to create objects dynamically.

In my example, an object meta contains the name for the constructor function to be used during initialization Object.create().

At the moment using the following code, I am able to create the objects dynamically but the property name is not defined.

I need that property on the result;

What is wrong in my script? Do you know a better way to achieve the same result?

      (function () {
            var costructors = {
                A: function () {
                    this.name = 'A';
                    console.log(this.name);
                },
                B: function () {
                    this.name = 'B';
                    console.log(this.name);
                },
                C: function () {
                    this.name = 'C';
                    console.log(this.name);
                }
            },
            meta = {
                A: true,
                B: true,
                C: true,
            },
            result = [];
            function createObjs() {
                Object.keys(meta).forEach(function (type) {
                    var obj = Object.create(costructors[type].prototype);
                    result.push(obj);
                }.bind(this));
            }
            createObjs.call(this);
            console.log(result);
        })();

Why the .bind(this) on the anonymous function of .forEach()? — Andreas
– Andreas, Commented Jul 17, 2015 at 13:08

Andreas · Accepted Answer · 2015-07-17 13:04:17Z

1

You haven't defined a prototype for any of the constructors, so you're not creating the name in your instances, since you're creating an object from their prototype, not from their constructor. Try

Object.create(constructors[type])

edited Jul 17, 2015 at 13:04

Andreas

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answered Jul 17, 2015 at 13:02

Shilly

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Comments

leo.fcx · Accepted Answer · 2015-07-17 13:07:53Z

1

An alternative without using Object.create would be:

var obj = new costructors[type]();

instead of:

var obj = Object.create(costructors[type].prototype);

answered Jul 17, 2015 at 13:07

leo.fcx

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Comments

Stephan Max · Accepted Answer · 2015-07-17 13:22:04Z

0

Actually, Object.create does not call the constructor function, but only creates a new object from the given prototype. Any member variables can be provided via a property object:

var obj = Object.create(
  constructors[type].prototype,
  { 'name' : { value: 'A', writable: true}}
);

answered Jul 17, 2015 at 13:22

Stephan Max

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