Why can't assign values ​​via for in in typescript?

Question

JavaScript

What's the right way to do things like this?

constructor(recipeDetails: { title?: string, description?: string } = { title: "", description: "" }) {
    for (let key in recipeDetails) {
      this[key.toString()] = recipeDetails[key];
    }
  }

Answer 1

constructor(recipeDetails: Details = { title: "", description: "", ingredients: [] }) {
    for (let key in recipeDetails) {
      (this[key as keyof Details] as Details[keyof Details]) = recipeDetails[key as keyof Details];
    }
  }

 interface Details { title?: string, description?: string, ingredients?: RecipeIngredient[]}

Answer 2

Why such difficulties? Enough . Object.assign(this, recipeDetails)