ES6 使用 NodeJS 逐行读取文件内容

比眉伴天荒 2022-03-18 16:47 514阅读 0赞

请参考：  
[ES5 使用 NodeJS 逐行读取文件的内容][ES5 _ NodeJS]  
[简单搭建 ES6 的运行环境][ES6]

在 ES6 中使用 NodeJS 实现逐行读取文件内容，具体代码实现如下：

先看一下目录结构：  
![在这里插入图片描述][20190221152310757.]

//ObserverMode.js
    
    const queuedObservers = new Set();
    
    const observe = fn => queuedObservers.add(fn);
    const observable = obj => new Proxy(obj, { set});
    
    function set(target, key, value, receiver) { 
        const result = Reflect.set(target, key, value, receiver);
        queuedObservers.forEach(observer => observer());
        return result;
    }
    
    const person = observable({ 
        name: '张三',
        age: 20
    });
    
    function print() { 
        console.log(`${ person.name}, ${ person.age}`)
    }
    
    observe(print);
    person.name = '李四';

//readFileByLine.js
    import fs from "fs";
    import readLine from "readline";
    
    const init = Symbol("init");
    const readObj = Symbol("readObj");
    
    class ReadFileByLine { 
    
        constructor(file) { 
            this.file = file;
        }
    
        read(cb) { 
            this[init]();
    
            this[readObj].on("line", cb);
    
            this[readObj].on("close", () => { 
                console.log("readLine closed ....");
            });
        }
    
        //私有方法
        [init]() { 
            //私有变量
            this[readObj] = readLine.createInterface({ 
                input: fs.createReadStream(this.file)
            });
        }
    }
    
    export default ReadFileByLine;

测试代码如下：

//readMyFile.js
    import ReadFileByLine from "./readFileByLine";
    
    const readFileByLine = new ReadFileByLine("ObserverMode.js");
    let idx = 0;
    readFileByLine.read((line) => { 
        var out = "line_" + idx + ": " + line.toString();
        console.log(out);
    });

通过使用 babel 将 ES6 转码成 ES5 之后，就可以正常运行了。

转码之后的代码如下：

//readFileByLine.js
    "use strict";
    
    Object.defineProperty(exports, "__esModule", { 
        value: true
    });
    
    var _createClass = function () {  function defineProperties(target, props) {  for (var i = 0; i < props.length; i++) {  var descriptor = props[i]; descriptor.enumerable = descriptor.enumerable || false; descriptor.configurable = true; if ("value" in descriptor) descriptor.writable = true; Object.defineProperty(target, descriptor.key, descriptor); } } return function (Constructor, protoProps, staticProps) {  if (protoProps) defineProperties(Constructor.prototype, protoProps); if (staticProps) defineProperties(Constructor, staticProps); return Constructor; }; }(); 
    var _fs = require("fs");
    
    var _fs2 = _interopRequireDefault(_fs);
    
    var _readline = require("readline");
    
    var _readline2 = _interopRequireDefault(_readline);
    
    function _interopRequireDefault(obj) {  return obj && obj.__esModule ? obj : {  default: obj }; }
    
    function _classCallCheck(instance, Constructor) {  if (!(instance instanceof Constructor)) {  throw new TypeError("Cannot call a class as a function"); } }
    
    var init = Symbol("init");
    var readObj = Symbol("readObj");
    
    var ReadFileByLine = function () { 
        function ReadFileByLine(file) { 
            _classCallCheck(this, ReadFileByLine);
    
            this.file = file;
        }
    
        _createClass(ReadFileByLine, [{ 
            key: "read",
            value: function read(cb) { 
                this[init]();
    
                this[readObj].on("line", cb);
    
                this[readObj].on("close", function () { 
                    console.log("readLine closed ....");
                });
            }
    
            //私有方法
    
        }, { 
            key: init,
            value: function value() { 
                //私有变量
                this[readObj] = _readline2.default.createInterface({ 
                    input: _fs2.default.createReadStream(this.file)
                });
            }
        }]);
    
        return ReadFileByLine;
    }();
    
    exports.default = ReadFileByLine;

//readMyFile.js
    "use strict";
    
    var _readFileByLine = require("./readFileByLine");
    
    var _readFileByLine2 = _interopRequireDefault(_readFileByLine);
    
    function _interopRequireDefault(obj) {  return obj && obj.__esModule ? obj : {  default: obj }; }
    
    var readFileByLine = new _readFileByLine2.default("ObserverMode.js");
    var idx = 0;
    readFileByLine.read(function (line) { 
        var out = "line_" + idx + ": " + line.toString();
        console.log(out);
    });

测试结果如下：

"D:\software\WebStorm 2017.2.4\bin\runnerw.exe" "D:\Program Files\nodejs\node.exe" D:\Workspaces\Webstorm\web\javascript\ES6\out\readMyFile.js
    line_0: 'use strict';
    line_0: 
    line_0: var queuedObservers = new Set();
    line_0: 
    line_0: var observe = function observe(fn) { 
    line_0:     return queuedObservers.add(fn);
    line_0: };
    line_0: var observable = function observable(obj) { 
    line_0:     return new Proxy(obj, {  set: set });
    line_0: };
    line_0: 
    line_0: function set(target, key, value, receiver) { 
    line_0:     var result = Reflect.set(target, key, value, receiver);
    line_0:     queuedObservers.forEach(function (observer) { 
    line_0:         return observer();
    line_0:     });
    line_0:     return result;
    line_0: }
    line_0: 
    line_0: var person = observable({ 
    line_0:     name: '张三',
    line_0:     age: 20
    line_0: });
    line_0: 
    line_0: function print() { 
    line_0:     console.log(person.name + ', ' + person.age);
    line_0: }
    line_0: 
    line_0: observe(print);
    line_0: person.name = '李四';
    readLine closed ....
    
    Process finished with exit code 0

[ES5 _ NodeJS]: https://blog.csdn.net/hsl0530hsl/article/details/87861701
[ES6]: https://blog.csdn.net/hsl0530hsl/article/details/87860839
[20190221152310757.]: /images/20220318/8a91f97a6b514160b5c09e4aae721592.png