nodejs-async：如何在 "async.series" 函数块中使用包含异步调用的循环

Question

在使用基于 async.series 的设计时，我必须在功能块中使用循环，如下所示：

var someFile = filePath;
async.series([
    function(cb) {
         _.forEach (
               someDataList,
               function (item) {
                   //call that executes out of sync
                   writeToFile(someFile,item)
                   //how to provide callback here
                   cb(); //<- is this correct - won't this take control out of this block in the very first loop iteration?
               }
         );
    }
],
//callback function
function (err) {...}
);

Answer 1

要探索有关异步的更多信息，您可以使用他们的方法 each。

Applies the function iteratee to each item in coll, in parallel. The iteratee is called with an item from the list, and a callback for when it has finished. If the iteratee passes an error to its callback, the main callback (for the each function) is immediately called with the error.

您的代码可以转换为：

var someFile = filePath;
async.series([
    function (cb) {
      async.each(someDataList, function (item, callback) {
        //call that executes out of sync
        writeToFile(someFile,item)

        // Execute internal callback for `async.each`
        callback()
      }, function (error) {
        if (error) {
          cb(error)
        } else {
          cb()
        }
      })
    }
  ],
//callback function
  function (err) {...
  }
);

但是，当然，您需要查看您的 writeToFile 功能。如果它是 sync 你需要将它包装在 try {} catch(e){} 构造和运行内部 callback() 中，在 catch 部分有错误 callback(error)。

Answer 2

您可以改用 forEachSeries。

var someFile = filePath;
async.forEachSeries(someDataList, function(item, cb) {
   writeToFile(someFile, item)
   cb();
},
//callback function
function () {...}
);

评论后更新：

不幸的是，无法在 forEachSeries 中获取迭代对象的索引。如果你想要 iteratee 的索引，你可以使用 eachOfSeries

var someFile = filePath;
async.eachOfSeries(someDataList, function(value, key, callback) {
    //Do something with key
    writeToFile(someFile, item)
    callback();
}, //callback function
function () {...}
);

nodejs-async：如何在 "async.series" 函数块中使用包含异步调用的循环

nodejs-async: How to use a loop containing an asynchronous call within an "async.series" function block

javascript

node.js

async.js