Promise 内没有 resolve 是种错误的写法 会编译报错 就如上面第二个和第四个
这里主要是 resolve 的问题 并不是直觉的返回了一个 promise 对象
文档里说的很清楚了 https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/resolve

The Promise.resolve() method returns a Promise object that is resolved with a given value. If the value is a promise, that promise is returned; if the value is a thenable (i.e. has a "then" method), the returned promise will "follow" that thenable, adopting its eventual state; otherwise the returned promise will be fulfilled with the value. This function flattens nested layers of promise-like objects (e.g. a promise that resolves to a promise that resolves to something) into a single layer.

所以看啥教程 直接读文档不就好了