javascript - 从原型(prototype)访问对象属性

Question

我有一个为 node.js 包装 mongodb 客户端的类。下面的类，当我调用 findUsers 时，我得到 this.collection 是未定义的。

如何从原型(prototype)访问 this.collection？

谢谢!

类:

var Users;

Users = (function () {

    function Users(db) {

        db.collection('users', function (err, collection) {
           this.collection = collection;
        });
    }

    Users.prototype.findUsers = function (callback) {

        this.collection.find({}, function (err, results) {

        });
    }

    return Users;

})();

用法:

//db holds the db object already created
var user = new Users(db);
user.findUsers();

Answer 1

你在原型(prototype)方法中做对了，你的错误在db.collection()的回调函数中。

var Users = (function () {
    function Users(db) {
        var that = this; // create a reference to "this" object
        db.collection('users', function (err, collection) {
            that.collection = collection; // and use that
        });
    }
    Users.prototype.findUsers = function (callback) {
        this.collection.find({}, function (err, results) {

        });
    }
    return Users;
})();