why typescript create duplicate assignment after compiling public parameter to constructor?

Question

I am new to typescript and was playing with compilation. Below file after compilation shows two assignments in js file, why is it so?

input file

class Student {
    constructor(public fname: string){
        this.fname = fname;
    }
}

output content

var Student = /** @class */ (function () {
    function Student(fname) {
        this.fname = fname;
        this.fname = fname;
    }
    return Student;
}());

Answer 1

TypeScript includes a concise way to create and assign a class instance property from a constructor parameter.

Which means, rather than:

class TestClass {
  public name: string;

  constructor(name: string) {
    this.name = name;
  }
}

one can use:

class TestClass {
  constructor(public name: string) { }
}

In your code snippet you are mixing both the syntax which is resulting in double assignment.