使用 async Node.js 简化Javascript代码，asyncnode.js

使用 async Node.js 简化Javascript代码，asyncnode.js

async Node.js

async 是Javascript的扩展库。它可以简化Node.js异步操作的书写，使代码更容易被读懂，而不是面对多层的括号发疯。

我们可以使用Node.js的包管理器npm直接安装它，在shell中输入：

12	npm install async

或者 更改package.json:

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{  "name": "application-name",  "version": "0.0.1",  "private": true,  "scripts": {    "start": "node ./bin/www"  },  "dependencies": {    ......        "async":"~0.9.0"  }}

然后运行 npm install. 安装完成后，在需要使用它的文件中加入:

12	var async = require('async');

series

使用series可以简化流程运行的异步函数。
现在构想一个这样的场景：
我需要执行一组动作，喝水 -> 吃饭 -> 打开电脑

通常的代码编写应该这样：

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function normalFunc() {    console.log("Normal function Run");    drinkWater(function (error,data) {        if(error) {            console.log("error: ",error,"msg: ",data);        } else {            console.log("drink water finish, I will eat food");            eatFood(function(error,data) {                if(error) {                    console.log("error: ",error,"msg: ",data);                } else {                    console.log("eat food finish, I will open mac");                    openMac(function(error,data) {                        if(error) {                            console.log("error: ",error,"msg: ",data);                        } else {                            //do something after open mac                            console.log("Mac is open, all action done");                        }                    });                }            });        }    });}

当异步调用超过两次嵌套，代码会变得不直观。使用async.series可以优化：

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function seriesFunc() {    async.series([        function(callback) {            console.log("Series function Run");            drinkWater(function(error,data) {                callback(error,data);            });        },        function(callback) {            console.log("drink water finish, I will eat food");            eatFood(function(error,data) {                callback(error,data);            });        },        function(callback) {            console.log("eat food finish, I will open mac");            openMac(function(error,data) {                callback(error,data);            });        }],        function(error,result) {            if(error) {                console.log("error: ",error,"msg: ",result);            }            else {                console.log("Mac is open, all action done");            }        }    );}

为了测试这个例子，我编写三个函数：

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function drinkWater(callback) {    callback(null,null);}function eatFood(callback) {    callback(null,null);}function openMac(callback) {    callback(null,null);}

接下来，我们测试这些函数，在console中的显示是下面的代码：

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Normal function Rundrink water finish, I will eat foodeat food finish, I will open macMac is open, all action done Series function Rundrink water finish, I will eat foodeat food finish, I will open macMac is open, all action done

这样看，我们达到了相同的效果。我们再测试出错的情况，将openMac函数更改成下面的代码：

1234	function openMac(callback) {    callback(1,"I can't find my mac");}

再测试这两个函数：

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Normal function Rundrink water finish, I will eat foodeat food finish, I will open macerror:  1 msg:  I can't find my mac Series function Rundrink water finish, I will eat foodeat food finish, I will open macerror:  1 msg:  [ null, null, 'I can\'t find my mac' ]

我们能发现 series 的 result是一个数组。series中的callback被执行后，无论动作的结果是成功还是失败，都会在result中添加一个数据。另一方面，我们也可以通过result中元素的数量，判断 series 执行了几个函数。

waterfall

另一个有用函数是 waterfall 。它和 series 一样，可以简化流程运行的异步函数。不同点是它可以在流程执行的过程中传递参数。

例如，我需要在异步函数中返回一些饮品或食物的信息，我需要更改

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function drinkWater(callback) {    callback(null,"Cola");}function eatFood(callback) {    callback(null,"Hamburger");}function openMac(callback) {    callback(null,"Chrome");}

然后添加：

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function waterFunc() {    async.waterfall([        function(callback) {            console.log("Water Fall Run");            drinkWater(function(error,data) {                callback(error,data);            });        },        function(data,callback) {            console.log("drink ",data," finish, I will eat food");            eatFood(function(error,data) {                callback(error,data);            });        },        function(data,callback) {            console.log("eat ",data," finish, I will open mac");            openMac(function(error,data) {                callback(error,data);            });        }],        function(error,result) {            if(error) {                console.log("error: ",error,"msg: ",result);            }            else {                 console.log("Mac ",result," is open, all action done");            }        }    );}

每一次运行函数的回调结果都会传给下一个动作，最后的result与series不同，是最后一次执行动作callback中传递的值。运行测试结果为：

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Water Fall Rundrink  Cola  finish, I will eat foodeat  Hamburger  finish, I will open macMac  Chrome  is open, all action done

然后再来测试出错的情况，更改：

1234	function eatFood(callback) {    callback(1,"not enough money");}

再运行的结果是：

1234	Water Fall Rundrink  Cola  finish, I will eat fooderror:  1 msg:  not enough money

总结

使用 async node.js 可以将复杂的逻辑表现的更直观。但如果逻辑只有一次回调，就不建议使用async了，我认为这会无意义的增加一些运行的成本。

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