如何在 Node.js 的 fs.readFile 中使用“this"引用 [英] How to use the 'this' reference in fs.readFile in Node.js

问题描述

我想使用我的 JavaScript 类的 this 关键字使用 fs.readFile 方法从文件中填充对象列表

I would like to populate a list of object from a file using the fs.readFile method using the this keyword of my JavaScript class

var MyReaderClass = (function() {
    //Const    

    function MyReaderClass() {
        this.readObjects = [];

        /**    
         * Default constructor for the MyReaderClass class
         */
        var _constructor = function() {

        }

        _constructor.call(this);
    }

    //Public    
    MyReaderClass.prototype.ReadFiles = function(p_path) {
        var files = fs.readdirSync(p_path);

        for (var i in files) {
            var fileName = files[i];
            fs.readFile(path.join(p_path, fileName), 'utf8', function(err, data) {
                if (err) {
                    return console.log(err);
                } 
                else {
                    var formattedData = /*... Logic to format my data into an object*/;
                    this.readObject.push(formattedData); //The "this" is not the reference to my class.
                }
            });
        }
    }
    return MyReaderClass;
})();

即使我正在创建此变量的本地实例(_self、that、instance 等)，在 readFile 方法之外，我的本地实例也获胜不会被填满.

Even if I'm creating a local instance (_self, that, instance, etc.) of my this variable, outside the readFile method, my local instance won't be filled up.

知道我如何做到这一点吗?

Any idea how I could accomplish this ?

推荐答案

readFile 是异步方法，您会丢失执行上下文.您需要将您的类绑定到 readFile 回调作为上下文.使用 Function.prototype.bind:

readFile is async method and you lose your execute context. You need bind your class to readFile callback as a context. Use Function.prototype.bind:

MyReaderClass.prototype.ReadFiles = function(p_path) {
    var files = fs.readdirSync(p_path);
    for (var i in files) {
        var fileName = files[i];
        fs.readFile(path.join(p_path, fileName), 'utf8', function(err, data) {
            /*readFile callback*/
        }.bind(this));//also here was a syntax error
    }
}

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