title: this is not defined error in javascript class constructor?
body: <p>I can't get my name parameter in my Employee class ! I don't know why I getting error like <strong><code>this is not undefined</code></strong> ! <code>this</code> is for current object right! I don't how to output my name parameter?</p>
  
  <pre><code>class Person {
      constructor(n, a) {
          var p = this;
          p.n = n;
          p.a = a;
          p.total = 0;
          p.a.map(x =&gt; 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());
  </code></pre>
  
  <p><em>Actual Output</em></p>
  
  <pre><code>Uncaught ReferenceError: this is not defined
  </code></pre>
  
  <p><em>Expected Output</em></p>
  
  <pre><code>My name is Min Min David  and My yearly income is 1333
  </code></pre>