带有承诺的 while 循环 [英] While loop with promises

问题描述

用 Promise 执行 while 循环之类的惯用方法是什么.所以:

What would be the idiomatic way to do something like a while loop with promises. So:

做点什么如果条件仍然存在，请再做一次重复然后做点别的.

do something if the condition still stands do it again repeat then do something else.

dosomething.then(possilblydomoresomethings).then(finish)

我已经这样做了，我想知道是否有更好/更惯用的方法?

I've done it this way I was wondering if there were any better/more idomatic ways?

var q = require('q');

var index = 1;

var useless =  function(){
        var currentIndex = index;
        console.log(currentIndex)
        var deferred = q.defer();
        setTimeout(function(){
            if(currentIndex > 10)
                deferred.resolve(false);
            else deferred.resolve(true);
            },500);
        return deferred.promise;
    }

var control = function(cont){
        var deferred = q.defer();
        if(cont){
                index = index + 1;
                useless().then(control).then(function(){
                        deferred.resolve();
                    });
            }
         else deferred.resolve();
        return deferred.promise;
    }

var chain = useless().then(control).then(function(){console.log('done')});

输出:1234567891011完成

Output: 1 2 3 4 5 6 7 8 9 10 11 done

推荐答案

我会使用一个对象来包装值.这样你就可以有一个 done 属性让循环知道你已经完成了.

I'd use an object to wrap the value. That way you can have a done property to let the loop know you're done.

// fn should return an object like
// {
//   done: false,
//   value: foo
// }
function loop(promise, fn) {
  return promise.then(fn).then(function (wrapper) {
    return !wrapper.done ? loop(Q(wrapper.value), fn) : wrapper.value;
  });
}

loop(Q.resolve(1), function (i) {
  console.log(i);
  return {
    done: i > 10,
    value: i++
  };
}).done(function () {
  console.log('done');
});

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