为什么`'foo" .bar = 42;`在ES6中以严格模式抛出`TypeError`？

问题描述：

根据ES5.1规范，程序use strict; foo.bar = 42; 导致创建一个 String 对象，分配给它上面的属性，然后抛弃该对象，导致没有可观察到的影响 - 包括任何例外。（没有效果可以通过在与Opera 12中的ES5兼容的JS实现中尝试来确认。）

According to the ES5.1 spec, the program "use strict;" "foo".bar = 42; causes a String object to be created, assigns to a property on it, and then throws the object away, resulting in no observable effects - including any exceptions. (The absence of effect can be confirmed by trying it in an ES5-compatible JS implementation like that in Opera 12.)

在现代JS实现中，它会抛出 TypeError 而不是试试：

In modern JS implementations, it throws a TypeError instead—try it:

"use strict"; "foo".bar = 42;

我很确定ES6规范规定了新的行为，但是尽管多次阅读相关部分，但我无法看到指定 TypeError 被抛出的位置。事实上，关键部分似乎是不变：

I am pretty sure the new behaviour is mandated by the ES6 spec, but despite reading the relevant sections several times I cannot see where it is specified that TypeError be thrown. In fact, the key parts appear to be unchanged:

6.2.3.2 PutValue（ V ， W ）＃

ReturnIfAbrupt（ V ）。

ReturnIfAbrupt（ W ）。

如果Type（ V ）不是Reference，则抛出 ReferenceError 异常。

让 base 为GetBase（ V ）。

如果IsUnresolvableReference（ V ）是的，然后是
- ...

ReturnIfAbrupt(V).
ReturnIfAbrupt(W).
If Type(V) is not Reference, throw a ReferenceError exception.
Let base be GetBase(V).
If IsUnresolvableReference(V) is true, then
- …

a。如果HasPrimitiveBase（ V ）为真，那么
- i。断言：在这种情况下， base 永远不会为null或未定义。
- ii。将 base 设置为ToObject（ base ）。
- a. If HasPrimitiveBase(V) is true, then
  - i. Assert: In this case, base will never be null or undefined.
  - ii. Set base to ToObject(base).
  规范（ES6或更高版本）在哪里强制抛出 TypeError ？
  
  Where does the spec (ES6 or later) mandate throwing TypeError?

答

我想它就在这里：

http://www.ecma-international.org/ecma-262/7.0/#sec-ordinaryset

9.1.9.1。 OrdinarySet（O，P，V，Receiver）

9.1.9.1. OrdinarySet (O, P, V, Receiver)

[...]

4.b。如果Type（Receiver）不是Object，则返回false。

4.b. If Type(Receiver) is not Object, return false.

（以前称为[[Set]]，在ES6§9.1.9。）

(Previously called [[Set]], in ES6 §9.1.9.)

虽然 PutValue 促销 base 到一个对象，它与接收者不一样 - GetThisValue（V）仍在原始 V （带有原始基数）。所以， GetThisValue 返回一个原语， OrdinarySet.4b 无法分配新创建的 ownDesc 并返回 false ，这反过来导致 PutValue.6d 抛出一个TypeError，提供参考是严格的。

Although PutValue promotes the base to an object, it doesn't do the same with the receiver -- GetThisValue(V) is still called on the original V (with a primitive base). So, GetThisValue returns a primitive, OrdinarySet.4b fails to assign a freshly created ownDesc and returns false, and this in turn causes PutValue.6d to throw a TypeError, provided the reference is strict.

V8的相应部分似乎遵循相同的逻辑：

The corresponding part of V8 seems to follow the same logic:

Maybe<bool> Object::AddDataProperty(....
  if (!it->GetReceiver()->IsJSReceiver()) {
    return CannotCreateProperty(...

https://github.com/v8/v8/blob/3b39fc4dcdb6593013c497fc9e28a1d73dbcba03/src/objects.cc#L5140

为什么`'foo" .bar = 42;`在ES6中以严格模式抛出`TypeError`？

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