Node.js全球范围

Question

Below is list of debugger queries, and responses, executed in a node.js at the global scope level:

 this.toString() "[object Object]" Object.getPrototypeOf(this).toString() "[object Object]" Object.getPrototypeOf(Object.getPrototypeOf(this)) null this.constructor function Object() { [native code] } Object.prototype.toString() "[object Object]" Object.prototype.toString.call(this) "[object Object]" Function.prototype.toString() "function () {}" Function.prototype.toString.call(this) TypeError: Function.prototype.toString is not generic 

The first set of responses suggests that the global scope is represented by an object that extends Object.prototype, as might be expected. So I'd expect that calling Function.prototype's .toString() on this would fail, as indeed it does (see the last query). I was expecting the query preceding that to pass an implicit this and so fail likewise, but it returns function () {} .

Why the difference, and what function is being referenced in the response?

Answer 1

In a function call, this is bound to either the object that "the function was called on" or the global object, for example:

const obj = {
  foo() {
    console.log(this);
  },
};

obj.foo(); // this is bound to obj
const obj2 = {};
obj2.bar = obj.foo;
obj2.bar(); // this is bound to obj2
const g = obj.foo;
g(); // this is bound to the global object

Therefore, Function.prototype.toString() is exactly the same as Function.prototype.toString.call(Function.prototype) . That's the matter of implementation of this function that it throws if called on anything other than a Function.