理解 JavaScript 的 this 关键字

贴此图，作为  [译]理解Javascript关键字this 的注解，此图也参考了  11.2.3 Function Calls

11.2.3 Function Calls # Ⓣ 

The production CallExpression : MemberExpression Arguments is evaluated as follows:

1. Let ref be the result of evaluating MemberExpression.

2. Let func be GetValue(ref).

3. Let argList be the result of evaluating Arguments, producing an internal list of argument values (see 11.2.4).

4. If Type(func) is not Object, throw a TypeError exception.

5. If IsCallable(func) is false, throw a TypeError exception.

6. If Type(ref) is Reference, then

   1. If IsPropertyReference(ref) is true, then

      1. Let thisValue be GetBase(ref).

   2. Else, the base of ref is an Environment Record

      1. Let thisValue be the result of calling the ImplicitThisValue concrete method of GetBase(ref).

7. Else, Type(ref) is not Reference.

   1. Let thisValue be undefined.

8. Return the result of calling the [[Call]] internal method on func, providing thisValue as the this value and providing the list argList as the argument values.

The production CallExpression : CallExpression Arguments is evaluated in exactly the same manner, except that the containedCallExpression is evaluated in step 1.

NOTE The returned result will never be of type Reference if func is a native ECMAScript object. Whether calling a host object can return a value of type Reference is implementation-dependent. If a value of type Reference is returned, it must be a non-strict PropertyReference.