在nodejs / async中提升的JavaScript变量 [英] JavaScript variables hoisting in nodejs/async

问题描述

在下一个示例中，我无法访问函数fetcher，parser和saveToDb中的变量locals。

var parser = require('parser.js');
var fetcher = require('fetcher.js');
var saveToDb = require('models/model.js');
var async = require('async');


function task() {
    var locals = []    //<-- declared here
    async.series([
        fetcher,    //<--  can not access "locals"
        parser,     //<--  can not access "locals"
        saveToDb    //<--  can not access "locals"
    ],
            function (err) {
                if (err) return callback(err);
                callback(null);
    });
}

在下一个示例中local可以访问。我只是从请求的模块中复制了函数声明，并将它们直接粘贴到async.series中。

In the next example "local"s is accessible. I just copyed the functions declarations from the requested modules, and pasted them straight inside "async.series".

var async = require('async');

function task() {
    var locals = []    //<-- declared here
    async.series([
        function(callback) {// <-- can access "locals"},  
        function(callback) {// <-- can access "locals"},
        function(callback) {// <-- can access "locals"}
    ],
            function (err) {
                if (err) return callback(err);
                callback(null);
    });
}

虽然这有效但我确实希望保持我的代码模块化。
如何解决这个问题？ 或 - 我在这里忘记了JavaScript的基础知识？

While this works - I do want to keep my code modular. How can I fix that ? Or - what I forgot here about the fundamentals of JavaScript ?

谢谢。

推荐答案

在第一个例子中，回调直播在另一个范围内，因此无法访问本地人。

In the first example, the callbacks live in another scope so can't access locals.

您可以创建获得<$ c $的部分函数c> locals 作为第一个参数传递的变量，但这需要你重写你的回调。

You could create partial functions that get the locals variable passed as first argument, but that would require you to rewrite your callbacks.

// creating a partial
async.series([
  fetcher.bind(fetcher, locals),
  parser.bind(parser, locals),
  saveToDb.bind(saveToDb, locals)
], ...)

// new function signatures
function fetcher (locals, callback) { ... }
function parser  (locals, callback) { ... }
function saveToDb(locals, callback) { ... }

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