参数未通过两个级别的JavaScript构造函数传递

Question

When running the below code I am receiving a type error when passing my arguments. It seems I am unable to pass my JSON data as arguments to the Employee object.

This is the error I am receiving:

/home/ubuntu/test/tests/employee.js:4
     this.name = params['name'] || "";
                  ^
TypeError: Cannot read property 'name' of undefined

Below is the code:

//comment

var Employee = function (params) {
    this.name = params['name'] || "";
    this.dept = params['dept'] || "general";
}

function Manager () {
    this.reports = [];
}
Manager.prototype = new Employee;

function WorkerBee (params) {
    console.log("params "+params);
    this.base = Employee;
    this.base(params);
    //    this.projects = params['projs'] || [];                                                                                                                                      
}

WorkerBee.prototype = new Employee;

function Engineer (params) {
    this.base = WorkerBee;
    this.base(params);
    params['projs']="engineering";
    //    this.base(params['name'], "engineering", params['projs']);                                                                                                                  
    this.machine = params['mach'] || "";
}
Engineer.prototype = new WorkerBee;


var jane = new Engineer({'name': "Doe, Jane", 'projs':["navigator", "javascript"], 'mach':"belau"});
console.log(jane);

Any guidance would be appreciated to correct this example.

Answer 1

That's exactly why you should not create a new instance of the parent when you want to establish inheritance: If the constructor expects an argument, what do you pass?

You should be using Object.create instead:

Child.prototype = Object.create(
  Parent.prototype,
  {constructor: {value: Child, configurable: true, writable: true}}
);

You also have to call the parent constructor as

Parent.call(this, arg1, arg2, ...);

inside the child constructor. While

this.base = WorkerBee;
this.base(params);

does work, it's a bit unconventional.

---

More info in: Benefits of using `Object.create` for inheritance