5

Let's take the following code:

var obj = {};
var x = Symbol();
Object.defineProperties(obj, {
  [x]: {
    value: true,
    writable: true
  },
  "property2": {
    value: "Hello",
    writable: false
  }
  // etc. etc.
});
console.log(obj[x])

Is this valid?

With the native Object.defineproperties code we get in the console.log true.

With the polyfill of zone.js

which is of the form of :

  Object.defineProperties = function (obj, props) {
    Object.keys(props).forEach(function (prop) {
      Object.defineProperty(obj, prop, props[prop]);
    });
    return obj;
  };

we get for the same code of console.log undefined.

This is because of the Object.keys function. I googled around and did not find in any place if this should be allowed or not.

Bergi
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David Michael Gang
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    Syntactically it's valid, practically it is as any other object key is converted to a string, like `Symbol()` (that would be the exact key name in this case). If you really want to be able to key by an arbitrary object - use the ES2015 `Map()` – zerkms Mar 20 '16 at 08:22
  • Uh, you're not defining a property **on** the symbol here? – Bergi Mar 20 '16 at 11:54

1 Answers1

2

I googled around and did not find in any place if this should be allowed or not.

You can always check the spec, in this case § 19.1.2.3 Object.defineProperties(O, Properties).

It uses the OwnPropertyKeys internal method, which does indeed list all string and symbol keys of an object.

This is because of the Object.keys function

Correct. It should be Object.getOwnPropertyNames(props).concat(Object.getOwnPropertySymbols(props)) instead. You may want to file a bug with zone.js. I do however wonder why you'd need a polyfill for the ES5 Object.defineProperties function when you're working with ES6 symbols?

Bergi
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  • But the polyfill shouldn't be applied in an ES6 environment where `Object.defineProperties` is already natively defined? – Bergi Mar 20 '16 at 12:07