javascript - jQuery 异步 ajax 调用

Question

我有以下带有列表的代码，并且对于该列表中的每个元素，执行 ajax 调用。

util.testMethod = function(list) {

            var map = new Map();

            list.forEach(function(data) {
                $.ajax({
                    url: 'https://......',
                    type: 'GET',
                    data: // data needed here
                    success: function(data) {
                        // do something
                    },
                    error: function(jqxhr, settings, exception) {
                        // dos omething
                    }
                });
            });


            return map;
        };

由于我正在进行大量异步 ajax 调用，因此我们假设其中 1 个调用需要很长时间才能执行。这个 testMethod 是否有可能在 ajax 调用完成之前返回？

Answer 1

当然。 ajax 调用是异步的，因此代码将继续执行，而无需等待成功/错误回调函数。

您有两个选择:

1. 将 ajax 调用作为同步调用(更多信息 here )
2. (推荐)使您的 testMethod 函数成为异步函数(更多信息 here )

但是(1°选项):

Setting async property to false is deprecated and in the process of being removed (link). Many browsers including Firefox and Chrome have already started to print a warning in the console if you use this:

下面是 2° 选项的示例(更多关于 here 中的 javascript Promise 和 here 中的 Promise.All ):

async function makeAjaxCall()  {
    return new Promise((resolve) => {
        setTimeout(() => {
            // Just to make the makeAjaxCall 1 second slower;
            $.ajax({
                url: 'http://www.mocky.io/v2/5e6ac7d32d0000db0c5fa686',
                type: 'GET',
                data: {},
                success: function(data) {
                    resolve(data);
                },
                error: function(jqxhr, settings, exception) {

                     resolve({ error: 'OMG an ERROR!'});
                    // dos omething
                }
            })
        }, 1000);
    });      
};

async function asynCall() {
  for(let i=0; i<10; i++) {
      // You can see in here that will wait 1 second before is going to the next ajax call
      const result = await makeAjaxCall();
      console.log(result);
  }
}

// You can run all your calls in paralel by using the Promise.All like this
async function promiseAll() {
  const ajaxCalls = [];
  for(let i=0; i<10; i++) {
      ajaxCalls.push(makeAjaxCall());
  }
  
  //for this case, the calls will be made in parallel, which measn will take slight more than 1 second 
  Promise.all(ajaxCalls).then(function(values) {
    // will print the array of values which contains the values of each ajax call
    console.log(values);
  });
}

asynCall();
promiseAll();

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