javascript - 我怎样才能摆脱这个 Promise for 循环？

Question

编辑:我知道如何使用 async/await 让它工作，但不幸的是，我无法使用它，因为它没有得到广泛支持(特别是 iOS 10、Internet Explorer 等)。所以我需要一种只有 promise 的方法。

我对 Promise 非常陌生，所以我陷入了困境。我有一个 for 循环，每当 i 等于 2 时我就想打破它(仅作为示例)。我尝试过输入 reject但它仍然继续直到 i<10 。我希望它在满足我的条件时停止。

for (let i = 0, p = Promise.resolve(); i < 10; i++) {
  p = p.then(_ => new Promise((resolve, reject) => {
    setTimeout(function() {
      console.log(i);
      if (i == 2) {
        reject("BREAK HERE");
      } else {
        resolve();
      }
    }, Math.random() * 1000)
  })).catch(err => {
    console.log(err);
  });
}

当前输出:

0
1
2
BREAK HERE
3
4
5
6
7
8
9

我希望它是:

0
1
2
BREAK HERE

Answer 1

只要不解析，序列就会停止

for (let i = 0, p = Promise.resolve(); i < 10; i++) {
  p = p.then(_ => new Promise((resolve, reject) => {
    setTimeout(function() {
      console.log("i",i);
      if (i == 2) {
        console.log("break here")
        
      } else {
        resolve();
      }
    }, Math.random() * 1000)
  })).catch(err => {
    console.log("err",err);
  });
}

但是由于此代码本身旨在对异步调用进行排序，因此应该考虑这样做:

// repeated call
next(
  0/*state*/, 
  i=>i<2/*match*/, 
  i=>i+1/*increment*/,     
  asyncCallPromisefied/*promise|promise[]*/, 
  [0]/*args*/
)
.catch(console.log)


// traverse array
next(
  0/*state*/, 
  i => i < 6/*match*/, 
  i => i + 1/*increment*/,
  asyncChain()/*promise|promise[]*/, 
  [0]/*args*/,
  0/*[promise[] index]*/
)
.catch(console.log)


// helper
function next(state, match, increment, action, args, pointer = 0/**inactive**/){
  if(match(state))
  if(Array.isArray(action)){
     
     return pointer < action.length
      ? action[pointer](...args)
      .then(i => next(
        increment(state), 
        match, 
        increment, 
        action, 
        [i],
        pointer + 1
      ))
      : undefined;
  } else {
    return action(...args)
    .then(i => next(
      increment(state), 
      match, 
      increment, 
      action, 
      [i]
    ))
  }
}



// wrapper
function asyncCall(i, callback){ 
  return setTimeout(() => {
    console.log(i == 2 ? 'break here': i);
    callback(null, ++i);
  }, Math.random() * 1000)
}

function asyncCallPromisefied(i){
  return new Promise(function(resolve, reject){
    asyncCall(i, function(err, args){
      if(err){
        reject(err)
      } else {
        resolve(args)
      }
    })
  })
}

function asyncChain(){return [
  function(i){console.log("chain",i);return Promise.resolve(i)},
  function(i){console.log("chain",i);return Promise.resolve(i)},
 function(i){console.log("chain",i);return Promise.resolve(i)},
  asyncCallPromisefied,
  function(i){console.log("chain",i);return Promise.resolve(i)},
]}