Is there any way to use a numeric type as an object key?

No, this is not possible. The key will always be converted to a string. See Property Accessor docs

Property names must be strings. This means that non-string objects cannot be used as keys in the object. Any non-string object, including a number, is typecasted into a string via the toString method.

> var foo = {}undefined> foo[23213] = 'swag''swag'> foo{ '23213': 'swag' }> typeof(Object.keys(foo)[0])'string'

In an object, no, but I have found Map extremely useful for this application. Here is where I have used it for numeric keys, a key-based event.

onKeydown(e) {  const { toggleSidebar, next, previous } = this.props;  const keyMapping = new Map([    [ 83, toggleSidebar ],  // user presses the s button    [ 37, next          ],  // user presses the right arrow    [ 39, previous      ]   // user presses the left arrow  ]);  if (keyMapping.has(e.which)) {    e.preventDefault();    keyMapping.get(e.which)();  }}

Appears to be by design in ECMA-262-5:

The Property Identifier type is used to associate a property name with a Property Descriptor. Values of the Property Identifier type are pairs of the form (name, descriptor), where name is a String and descriptor is a Property Descriptor value.

However, I don't see a definite specification for it in ECMA-262-3.Regardless, I wouldn't attempt to use non-strings as property names.