Assignments to global objects in Javascript should be global declarations

// @noEmit: true
// @allowJs: true
// @checkJs: true
// @Filename: a.js
global.x = 1
window.y = 2
this.z = 3

var n = x + y + z

Expected behavior: No error, and x, y and z are visible globally.

Actual behavior: Errors:

1. Can't find name 'global'
2. 'Window' has no property 'y'
3. Cannot find name 'x', 'y' or 'z'

Ideally, global should only be visible when targetting node and window should only be visible when targetting the browser. It's not a requirement, though.