How to new WeakMap with array as parameter?

Question

I have been reading MDN docs about WeakMap. And it mentions the syntax:

new WeakMap([iterable])

But when I tried this, error occurred:

var arr = [{a:1}];
var wm1 = new WeakMap(arr);

Uncaught TypeError: Invalid value used as weak map key

Could you please offer me an example about how to do it via an array?

Answer 1

The documentation says:

Iterable is an Array or other iterable object whose elements are key-value pairs (2-element Arrays).

{a: 1} is an object, not a 2-element array.

Further down it says:

Keys of WeakMaps are of the type Object only.

So you can't use a string as a key in a WeakMap.

Try:

var obj = {a:1};
var arr = [[obj, 1]];
var wm1 = new WeakMap(arr);
console.log(wm1.has(obj));