js: ref object assignment silently gives wrong results

[timotheecour]

js: ref object assignment incorrect (related to #14339 which was fixed in #16002, but for js backend)

Example

block:
  type
    Node = ref object
      val: int
  proc bar(c: Node): var int =
    var n = c
    n.val
  var a = Node(val: 3)
  a.bar() = 5
  doAssert a.val == 5 # fails, got 3

Current Output

fails

Expected Output

works

Additional Information

• devel 1.5.1 c39fa0d
• found while working on fix #14339, #13511, #14420: fixes limited VM support for addr #16002; after that PR, it works for c,cpp,vm,js at CT, but not js

[metagn]

Generated code (mangle numbers removed):

function bar(c) {
  var result = null;
  var result_Idx = 0;

    var n = c;
    result_Idx = [, n.val];
    result = n.val;
    result[result_Idx] = n.val;

  return [result, result_Idx];

}