在继续循环之前完成回调？

Question

所以我已经坚持了一段时间。如果有人可以帮助我解决这个问题，我将不胜感激！我想要的是让我的函数及其回调在继续循环之前完成。在用户在文本区域中输入英文文本并单击翻译按钮后，我调用“translate_all”。 （“方法”，“g_loop”，“g_where”和“go”是全局变量。）最终我想要的是让输入的英文短语翻译成数组中的下一种语言，然后把它翻译回英文看看如果有差异，然后继续浏览所有语言。

我尝试过承诺，但老实说，我无法理解它。我尝试了这种“hackish”方法，将循环捕获在一个while循环中，直到全局变量“go”在回调之后发生变化。但是，发生的事情是当我运行它时浏览器冻结，我认为这是因为虽然该方法阻止循环继续，但它是如此卡在循环中，以至于它永远不会从回调中接收到“go”已更改的消息.也许我可以像很快向我推荐的那样做某种事件监听器，但我不确定。我觉得我是如此接近，它让我疯狂地试图让它工作这么长时间。任何和所有的帮助表示赞赏！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

您可以创建一个按顺序运行的承诺链，如下所示：

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，并且您提供了回调承诺。 使用这种方法或多或少会转化为：

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