CODEWITHSUNDEEP
javascriptnode.jstypescript
Ken Zira
Ken Zira

Reputation: 1176

Typescript map function return new object not working

I'm new to typescript

export class Reward {
    id: number;
    point: number;
    status: Status;


    constructor(id: number, point: number, status: Status) {
        this.id = id;
        this.point = point;
        this.status = Status.NONE;
    }

}

export enum Status {
    CLAIMED,
    AVAILABLE,
    NONE
}



   public getRewardsOf(numberOfDay: number): Array<Reward> {
       return this.availableRewards.map((reward: Reward, index: number) => {
            if (index == (numberOfDay - 1)) {
                return new Reward(reward.id, reward.point, Status.AVAILABLE);
            } else {
                return reward;
            }
        });
    }

the if doesn't work for me. It still returns the same old object (the status value is the same). it's supposed to be different even though I create a new object.

It works when I use

 if (index == (numberOfDay - 1)) {
         return {
                    'id': reward.id,
                    'point': reward.point,
                    'status': Status.AVAILABLE
                };
            } else {
                return reward;
            }

if so I lose the power of typescript

Upvotes: 2

Views: 1077

Answers (1)

jagthebeetle
jagthebeetle

Reputation: 715

Your constructor is hardcoding the value Status.NONE:

...
this.status = Status.NONE
...

This will effectively discard the status argument passed to the constructor.

If you wish to provide Status.NONE as a default parameter, do:

    constructor(id: number, point: number, status = Status.NONE) {
        this.id = id;
        this.point = point;
        this.status = status;
    }

You can further reduce this to:

    constructor(public id: number, public point: number,
                public status = Status.NONE) {
    }

Edit: Also, because TypeScript is structurally, not nominally typed (see structural typing), you don't lose any type safety by returning a literal versus a class-constructed instance. Both versions of your code can safely be said to be returning a Reward. TS Playground

class Reward {
  constructor(public id: string) {}
}

// This is OK.
const x: Reward = {id: '12435'};

If Reward starts adding methods, then what you lose is the ability to create a Reward easily with your object literal.

Upvotes: 5

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