CODEWITHSUNDEEP
arraystypescriptobjectforeach
Manish Shrestha
Manish Shrestha

Reputation: 440

How to assign properties of objects in an array to multiple class properties?

I have a typescript class with 2 private properties and an array of objects.

class AssigningProperties {
  private animalType1: string;
  private animalType2: string;

  animals = [
    {
      name: "Bob",
      type: "cat"
    },
    {
      name: "Max",
      type: "dog"
    }
  ];

  constructor() {
    this.animals.forEach(v => console.log(v.name));
  }
}

new AssigningProperties ();

I want to assign the class property animalType1 to cat and animalType2 to dog, preferably using Array.foreach.

I can assign it using index of the objects like so: this.animalType1 = this.animals[0].type; but I feel there's a better approach. Help?

Link to CodeSandBox

Upvotes: 2

Views: 1015

Answers (1)

T.J. Crowder
T.J. Crowder

Reputation: 1075855

What you're doing is fine, but if you want to do it in a loop, make animalTypes an array:

private animalTypes: string[];

Then you'd use the second parameter for the forEach callback, which is the index of the entry:

this.animals.forEach((v, i) => v.type = this.animalTypes[i]);

Or if you meant that you wanted to assign "cat" to the first animalTypes (which is what your CodeSandbox code is doing), then:

this.animals.forEach((v, i) => this.animalTypes[i] = v.type);

With either of those, you'll end up with the type stored in two places, which creates a maintenance hazard — you can update animals[0].type without updating animalType1/animalTypes[0].

Assuming you wanted animals to be the one source of truth, you might use getters instead:

private get animalType1(): string {
 return this.animals[0].type;
}
private get animalType2(): string {
  return this.animals[1].type;
}

Live Copy on the playground

Or for the animalTypes approach, you'd use a Proxy:

interface Animal {
  name: string;
  type: string;
}
class AssigningProperties {
  animals: Animal[] = [
    {
      name: "Bob",
      type: "cat"
    },
    {
      name: "Max",
      type: "dog"
    }
  ];
  private animalTypes = new Proxy<Animal[]>(this.animals, {
    get(target, propName) {
      if (propName in target) {
        return Reflect.get(target, propName).type;
      }
      return undefined;
    }
  });
}

Live Copy on the playground

Upvotes: 2

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