Proposal static type constraints features

[YU HengChun]

You mean this...

The original:

```js
function f(x) {
  return typeof x !== 'string' || typeof x === 'undefined'; 
}
```

The proposal:

```js
function f(x = void String) {
  void Boolean; // The complete code should be like this
  return typeof x !== 'string' || typeof x === 'undefined'; 
}
```

Thank you, you actually provided an example to prove that the proposal is conflict-free.

Test code is casually written, the results of these two versions will be consistent.


我得谢谢你的关注(真的, 这样才可以有更多的验证).
你刚好提供了一个例子证明我的提案是无冲突的.
随便写测试代码吧, 这两个版本的结果完全一致.

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