在继续循环之前，获取要完成的回调

Question

所以我在这方面已经有一段时间了。如果有人能帮我解决这个问题，我将非常感激！我想要的是在循环中继续之前完成我的函数及其回调。在用户在文本区域输入英文文本并单击翻译按钮后，我称之为"translate_all"。（"Method"、"g_loop"、"g_where"one_answers"go"是全局变量。）最终，我想要的是将输入的英语短语翻译成数组中的下一种语言，然后将其翻译回英语，看看是否有差异，然后继续使用所有语言。

我试过promise，但老实说，我无法理解它。我尝试了这种"疯狂"的方法，将循环困在while循环中，直到回调后全局变量"go"发生变化。但是，当我运行这个程序时，浏览器会冻结，我认为这是因为尽管这种方法阻止了循环的继续，但它被困在循环中，以至于它从未从回调中收到"go"被更改的消息。也许我可以做一些很快推荐给我的事件监听器，但我不确定。我觉得我离得太近了，想让这件事持续这么长时间，真让我抓狂。感谢您的帮助！谢谢

我有这个：

var translate_all = function translate_all () {
  // set global g_where to this div to append an image
  g_where = $("#g_div");
  g_where.append("<img alt='Google Logo' src='/img/google_g_medium.png'/><br>");
  // get the text the user input
  var a_text = $("#accuracy_text").val();  
  // translation codes for api
  var language_codes = ["en", "ar", "bg", "ca", "hr", "cs", "da", "nl", "et", "fi", "fr", "de", "el", "ht", "id", "it", "ko", "lv", "lt", "ms", "mt", "no", "fa", "pl", "pt", "ro", "ru", "sl", "sl", "es", "th", "tr", "uk", "ur", "vi"]; 
  // set global g_loop to what text the user input
  g_loop = a_text;
  // start a loop
  for (var i = 1; i < language_codes.length; i++)
  {
    // error checking and trying to debug and see what is wrong
    console.log("working")
    // define which callback i want to run
    method = 2;
    // this callback sets the response from google placed in g_response to g_loop; it translates from one language in loop to the next
    GoogleTranslate(g_loop, language_codes[i-1], language_codes[i]);
    console.log("continue");
    // THIS is where i try to get the loop to stop until the callback has run because this loop is only able to break when the callback has finished
    while (go == 0)
    {
      if (go == 1)
      {
        break;
      }
    }
    // set go back to zero
    go = 0;
    // set g_where and append the response to the div
    g_where = $("#g_div");
    g_where.append(g_response)
    method = 1;
    // this translates the initial response back to english to see if there is a difference and appends it to the div
    GoogleTranslate(g_loop, language_codes[i], "en");
    // trying to make sure the callback is executed again before continuing
    while (go == 0)
    {
      if (go == 1)
      {
        break;
      }
    }
    go = 0;
  }
}

function GoogleTranslate (text, from, to) {
  var newScript = document.createElement('script');
  var sourceText = escape(text);
  newScript.type = 'text/javascript';
  var APIKEY = 'my api key';
  var source = 'https://www.googleapis.com/language/translate/v2?';
  source += 'key=' + APIKEY;
  source += '&source=' + from;
  source += '&target=' + to;
  source += '&callback=google_translation';
  source += '&q=' + sourceText;
  newScript.src = source;
  console.log("sent");
  // send the reuqest to google api
  $('head')[0].appendChild(newScript); 
}

// callback
function google_translation(response) {
  g_response = response.data.translations[0].translatedText;
  if (method == 0)
  {
    // replaces text in a given location (not for code shown)
    g_where.val(g_response);
    console.log("0");
  }
  if (method == 1)
  {
    // appends text in a given location
    g_where.append(": " + g_response + "<br>");
    console.log("1");
  }
  if (method == 2)
  {
    // sets variable to response
    g_loop = g_response;
    console.log("2");
  }
  go = 1;
  console.log("translated");      
}

Answer 1

您可以创建一个承诺链，它将按如下顺序运行：

myList.reduce((promise, item) => {
  return promise.then(() => new Promise((resolve, reject) => {
    // do whatever you need to do here
    // resolve when finished with this iteration.
  }))
}, Promise.resolve());

因此，假设您有一个类似[1,2,3]的列表，并且您给出了回调承诺。使用这种方法或多或少可以转化为：

Promise.resolve()
  .then(1 => function () { })
  .then(2 => function () { })
  .then(3 => function () { });