error in typescript for each loop syntax

Question

I'm trying to make a class with typescript 2.0.3 but I have some problems and I don't know why.

this is my code

import { Component, OnInit } from '@angular/core'; 
import {Car} from '../interfaces/car';

class PrimeCar implements Car 
{
  constructor(public vin, public year, public brand, public color) {}
}
@Component({
  selector: 'rb-test',
  templateUrl: './test.component.html',
  styleUrls: ['./test.component.css']
})
export class TestComponent implements OnInit {
  displayDialog: boolean;
  car: Car = new PrimeCar(null, null, null , null);
  selectedCar: Car;
  newCar: boolean;
  cars: Car[];
  constructor() { }
  ngOnInit() {
this.cars = [ {vin: '111', year: '5554' , brand: '5646' , color: '6466' },
              {vin: '111', year: '5554' , brand: '5646' , color: '6466' },
              {vin: '111', year: '5554' , brand: '5646' , color: '6466' },
              {vin: '111', year: '5554' , brand: '5646' , color: '6466' }
             ];
  }    
  showDialogToAdd() {
    this.newCar = true;
    this.car = new PrimeCar(null, null, null, null);
    this.displayDialog = true;
  }
  save() {
    const cars = [...this.cars];
    if (this.newCar) {
      cars.push(this.car);
    } else {
      cars[this.findSelectedCarIndex()] = this.car;
    }
    this.cars = cars;
    this.car = null;
    this.displayDialog = false;
  }
  delete() {
    const index = this.findSelectedCarIndex();
    this.cars = this.cars.filter((val, i) => i !== index);
    this.car = null;
    this.displayDialog = false;
  }
  onRowSelect(event) {
    this.newCar = false;
    this.car = this.cloneCar(event.data);
    this.displayDialog = true;
  }    
  cloneCar(c: Car): Car {
    const car = new PrimeCar(null, null, null, null);
    for (let  prop: string in c) {
      car[prop] = c[prop];
    }
    return car;
  }
  findSelectedCarIndex(): number {
    return this.cars.indexOf(this.selectedCar);
  }
}

In the cloneCar method, I have this error when trying to write:

for (let  prop: string in c) {
...}

Tslint: identifier 'prop' is never reassigned ,use const instead of let

this is an image capture from my IDE: see error here

NB: I'm using this code in angular project version 2.3.0

Some help, please!

Answer 1

Your IDE is right. You are declaring prop with let and not with const.

let is for variables that are subject to change. For example:

let x = 5;
x = 7;

We declared x and then we changed it's value.

const is for values that won't change. For example:

const x = 5;
x = 7; // Throws an error.

So, in your case, as prop doesn't and won't change, has to be a constant (const):

for (const  prop: string in c) {
...}

Check this documentation for a deeper understanding.