ES5 使用 NodeJS 逐行读取文件的内容

不念不忘少年蓝@ 2022-03-18 16:37 346阅读 0赞

参考：  
[ES6 使用 NodeJS 逐行读取文件内容][ES6 _ NodeJS]

在 ES5 中使用 NodeJS 逐行读取文件的内容，下面是具体的代码实现。

目录结构如下  
![在这里插入图片描述][20190221151450428.]

//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
    (function (global) { 
        var fs = require("fs");
        var readLine = require("readline");
    
        function readByLine(file, cb) { 
            var is = fs.createReadStream(file);
    
            var readObj = readLine.createInterface({ 
                input: is
            });
    
            readObj.on("line", cb);
    
            readObj.on("close", () => { 
                console.log("readLine closed ....");
            });
        }
        global.readFileByLine = readByLine;
    })(global);
    
    var idx = 0;
    readFileByLine("ObserverMode.js", function (line) { 
        var out = "line_" + idx++ + ": " + line.toString();
        console.log(out);
    });

直接 Run ‘readFileByLine.js’

最后输出结果如下：

"D:\software\WebStorm 2017.2.4\bin\runnerw.exe" "D:\Program Files\nodejs\node.exe" D:\Workspaces\Webstorm\web\javascript\ES6\src\readFileByLine.js
    line_0: 
    line_1: const queuedObservers = new Set();
    line_2: 
    line_3: const observe = fn => queuedObservers.add(fn);
    line_4: const observable = obj => new Proxy(obj, { set});
    line_5: 
    line_6: function set(target, key, value, receiver) { 
    line_7:     const result = Reflect.set(target, key, value, receiver);
    line_8:     queuedObservers.forEach(observer => observer());
    line_9:     return result;
    line_10: }
    line_11: 
    line_12: const person = observable({ 
    line_13:     name: '张三',
    line_14:     age: 20
    line_15: });
    line_16: 
    line_17: function print() { 
    line_18:     console.log(`${ person.name}, ${ person.age}`)
    line_19: }
    line_20: 
    line_21: observe(print);
    line_22: person.name = '李四';
    line_23: 
    readLine closed ....
    
    Process finished with exit code 0

[ES6 _ NodeJS]: https://blog.csdn.net/hsl0530hsl/article/details/87862013
[20190221151450428.]: /images/20220318/2ca50b744c3f4131a2db30884f865740.png