从[ajax]函数内部获取返回值

Question

how do I get the return value of "res" from the function. It shows undefined when i try to access it.

 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

You've to use either Promise or callback approach to achieve that. Promise is relatively new and not supported in all browsers.

Promise approach

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');
      }
    }
  });
}

How to get the response

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

Callback approach

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');
    }
  }
}

How to get response

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

Answer 2

You can try this way. Hope its works-

So your XHR function have one callback function to get the return value,

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);
     }
   }
}

when you are calling the XHR function:

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