What's the proper way of using property descriptors in Object.create?

Question

I passed an object as the second parameter in the Object.create method, but I'm getting the following error:

Uncaught TypeError: Property description must be an object: 1

Here's the faulty code:

var test = Object.create(null, {
    ex1: 1,
    ex2: 2,
    meth: function () {
        return 10;
    },
    meth1: function () {
        return this.meth();
    }
});

Answer 1

Object.create(proto, props) has two arguments:

1. proto — the object which should be the prototype of the newly-created object.
2. props (optional) — an object whose properties specify property descriptors to be added to the newly-created object, with the corresponding property names.

The format for the props object is defined here.

In short, the available options for each property descriptor are these:

{
    configurable: false, // or true
    enumerable: false, // or true
    value: undefined, // or any other value
    writable: false, // or true
    get: function () { /* return some value here */ },
    set: function (newValue) { /* set the new value of the property */ }
}

The problem with your code is that the property descriptors you've defined are not objects.

Here's an example of a proper usage of property descriptors:

var test = Object.create(null, {
    ex1: {
        value: 1,
        writable: true
    },
    ex2: {
        value: 2,
        writable: true
    },
    meth: {
        get: function () {
            return 'high';
        }
    },
    meth1: {
        get: function () {
            return this.meth;
        }
    }
});