节点 JS - TypeError：无法读取未定义的属性“CONTEXT_1”答案

【问题标题】：Node JS - TypeError: Cannot read property 'CONTEXT_1' of undefined节点 JS - TypeError：无法读取未定义的属性“CONTEXT_1”
【发布时间】：2018-05-21 21:17:56
【问题描述】：

文件名：orderManager.js

const notificationManager = require("./notificationManager");

var orderManager = (function() {

    function orderManager() {
        console.log("orderManager");
    };

    orderManager.bootstrap = function() {
        console.log("orderManager.bootstrap");
        return new orderManager();
    };

    orderManager.prototype.orderContext = {
        "CONTEXT_1": "context_1",
        "CONTEXT_2": "context_2",
        "CONTEXT_3": "context_3"
    };

    orderManager.prototype.notify = function() {
        var dataObj = {};
        notificationManager.sendToClient(dataObj);
    };

    return orderManager;

}());
module.exports = orderManager.bootstrap();

文件名：notificationManager.js

const orderManager = require("./orderManager");

var notificationManager = (function() {

    function notificationManager() {
        console.log("notificationManager");
    };

    notificationManager.bootstrap = function() {
        console.log("notificationManager.bootstrap");
        return new notificationManager();
    };

    notificationManager.prototype.sendToClient = function(dataObj) {
        console.log("notificationManager.prototype.sendToClient");

        var _this = this;
        switch (_this.request.body.orderContext) {
            case orderManager.orderContext.CONTEXT_1:
                notifyClient(_this, dataObj);
                break;

        }
    };

    return notificationManager;

}());
module.exports = notificationManager.bootstrap();

当我尝试从 orderManager.js 文件中调用 notificationManager.sendToClient() 函数时，会出现错误 TypeError: Cannot read property 'CONTEXT_1'的未定义。

【问题讨论】：

标签： node.js

【解决方案1】：

您不能将 orderManager.js 和 notificationManager.js 紧密耦合。

根据您的 sn-p，您正在尝试执行 orderManager.notify().

你的 Javascript 编译流程是这样的

需要 orderManager.js
在 orderManager.js 中需要 const notificationManager = require("./notificationManager");
在 notificationManager.js 中需要 const orderManager = require("./orderManager");
由于 orderManager.js 没有完全执行，它被分配了空对象 {} 而不是 orderManager const orderManager = {} // Not an instance of orderManager 的实例
由于分配了空对象，因此在访问 orderManager.orderContext.CONTEXT_1 时会抛出 undefined

这里我修改了你的 sn-p 并删除了 orderManager.js 中的 notificationManager.js 依赖

orderManager.js

  var orderManager = (function() {

        function orderManager() {
            console.log("orderManager");
        };

        orderManager.bootstrap = function() {
            console.log("orderManager.bootstrap");
            return new orderManager();
        };

        orderManager.prototype.orderContext = {
            "CONTEXT_1": "context_1",
            "CONTEXT_2": "context_2",
            "CONTEXT_3": "context_3"
        };

        return orderManager;

    }());
    module.exports = orderManager.bootstrap();

文件名：notificationManager.js

const orderManager = require("./orderManager");

var notificationManager = (function() {

    function notificationManager() {
        console.log("notificationManager");
    };

    notificationManager.bootstrap = function() {
        console.log("notificationManager.bootstrap");
        return new notificationManager();
    };

    notificationManager.prototype.sendToClient = function(dataObj) {
        console.log("notificationManager.prototype.sendToClient");

        var _this = this;
        switch (_this.request.body.orderContext) {
            case orderManager.orderContext.CONTEXT_1:
                notifyClient(_this, dataObj);
                break;

        }
    };

    return notificationManager;

}());
module.exports = notificationManager.bootstrap();

文件名：index.js

const a = require('./notificationManager');
a.sendToClient();

【讨论】：