从[AJAX]函数内部获取返回值

Question

如何从函数中获取" res"的返回值。当我尝试访问它时，它显示不确定。

function solution() {
  var url = "https://translate.yandex.net/api/v1.5/tr.json/translate",
    keyAPI = "abcdefgh"
  var xhr = new XMLHttpRequest(),
    textAPI = "some text",
    langAPI = "fr"
  data = "key=" + keyAPI + "&text=" + textAPI + "&lang=" + langAPI;
  xhr.open("POST", url, true);
  xhr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
  xhr.send(data);
  xhr.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {
      var res = this.responseText;
      return res;
    }
  }
}

Answer 1

您可以使用承诺或回调方法来实现这一目标。Promise相对较新，并且在所有浏览器中不支持。

承诺方法

function solution() {
  return new Promise(function(resolve, reject) {
    var url = "https://translate.yandex.net/api/v1.5/tr.json/translate",
      keyAPI = "abcdefgh"
    var xhr = new XMLHttpRequest(),
      textAPI = "some text",
      langAPI = "fr"
    data = "key=" + keyAPI + "&text=" + textAPI + "&lang=" + langAPI;
    xhr.open("POST", url, true);
    xhr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
    xhr.send(data);
    xhr.onreadystatechange = function() {
      if (this.readyState == 4) {
        var res = this.responseText;
        this.status == 200 ? resolve(res) : reject('error');
      }
    }
  });
}

如何获得响应

solution().then(function(res) {
  console.log(res);
}, function(err) {
  console.log(err);
});

回调方法

function solution(success, failure) {
  var url = "https://translate.yandex.net/api/v1.5/tr.json/translate",
    keyAPI = "abcdefgh"
  var xhr = new XMLHttpRequest(),
    textAPI = "some text",
    langAPI = "fr"
  data = "key=" + keyAPI + "&text=" + textAPI + "&lang=" + langAPI;
  xhr.open("POST", url, true);
  xhr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
  xhr.send(data);
  xhr.onreadystatechange = function() {
    if (this.readyState == 4) {
      var res = this.responseText;
      this.status == 200 ? success(res) : error('error');
    }
  }
}

如何获得响应

solution(function(res) {
  console.log(res);
}, function(err) {
  console.log(err);
});

Answer 2

您可以这样尝试。希望它的工作 -

因此，您的XHR功能具有一个回调函数以获取返回值，

function solution(callback) {
  var url = "https://translate.yandex.net/api/v1.5/tr.json/translate",
      keyAPI = "abcdefgh";
  var xhr = new XMLHttpRequest(),
      textAPI = "some text",
      langAPI = "fr";
  data = "key=" + keyAPI + "&text=" + textAPI + "&lang=" + langAPI;
  xhr.open("POST", url, true);
  xhr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
  xhr.send(data);
  xhr.onreadystatechange = function() {
  if (this.readyState == 4 && this.status == 200) {
       var res = this.responseText;
       callback(res);
     }
   }
}

当您调用XHR函数时：

solution(function(response){
  // you will get the response over here 
});