为什么我不能直接在 SetTimeout 函数中为 Promise 调用 resolve()

Question

I have two versions of a sleep function, one is waiting for the resolve the other isn't:

function sleephelper1(ms) {
    return new Promise(function(resolve) {
        setTimeout(() => resolve('done'), ms);
    })
  }

  function sleephelper2(ms) {
    return new Promise(function(resolve) {
        setTimeout(resolve('done'), ms);           
    })
  }

Then I call either sleephelper1 or sleephelper2:

async function test(){
var test = await sleephelper1(3000);
console.log(test)
console.log("exit test function")
  }

test()

The first one is waiting 3 seconds before in resolves. But sleephelper2 ist not working properly. The code gets executed immediatly. I thought that SetTimeout can delay the call of a function by a given amount of time. Is resolve() not a function ? I have found this post JavaScript promise resolving with setTimeout which is quite what I am asking here, exept that I am using async await. Also I did not get the explanation. Could somebody explain to me why this behaves the way it does ?

Answer 1

setTimeout(() => resolve('done'), ms);

This means "create a function with the text () => resolve('done') and pass it into setTimeout". setTimeout will wait the specified amount of time, and then call that function.

setTimeout(resolve('done'), ms);

This means "immediately call resolve('done') and pass its result into settimeout". the return value from resolve is undefined , so undefined is passed into setTimeout. There is thus no function for setTimeout to run 3 seconds later.