this is not defined error in javascript class constructor?

Question

I can't get my name parameter in my Employee class ! I don't know why I getting error like this is not undefined ! this is for current object right! I don't how to output my name parameter?

class Person {
    constructor(n, a) {
        var p = this;
        p.n = n;
        p.a = a;
        p.total = 0;
        p.a.map(x => p.total += parseInt(x)); //get total salary     
    }
    firstName() {
        return this.n = "Min Min ";
    }
    displayMsg() {
        return " and My yearly income is " + this.total;
    }
}

class Employee extends Person {
    constructor(name, age) {
        this.name = name;
    }
    lastName() {
        return this.name;
    }
    Show() {
        return "My name is " + super.firstName() + this.lastName() + super.displayMsg();
    }
}
emp = new Employee("David", [123, 456, 754]);
console.log(emp.Show());

Actual Output

Uncaught ReferenceError: this is not defined

Expected Output

My name is Min Min David  and My yearly income is 1333

The actual error I get in Firefox 48.0a2 is `ReferenceError: |this| used uninitialized in Employee class constructor`. — Sebastian Simon, Jun 29 '16 at 03:06
I have seen that duplicate question's answer and tested ! But get error in `.map` function. — Jack jdeoel, Jun 29 '16 at 03:17
It's ok now, under answer solved my question ! I just point out that duplicate question's answer doesn't solve my OP. — Jack jdeoel, Jun 29 '16 at 03:23
I think the difference is `super()` and `super(name,age)` ! If I just used `super()`, It is getting *Cannot read property 'map' of undefined* error . Using `super(name,age)` is worked. — Jack jdeoel, Jun 29 '16 at 03:30

score 14 · Accepted Answer · answered Jun 29 '16 at 03:09

14

You need to call the super() constructor first before you can continue instantiating your class:

class Employee extends Person {
    constructor(name, age) {
        super(name, age);
        this.name = name;
    }

    ...
}

JSBin

answered Jun 29 '16 at 03:09

TimoStaudinger

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this is not defined error in javascript class constructor?

1 Answers1