如何使用 typescript 返回一个导入数组类型的所有项之和？

Question

I am stuck on making a method that is supposed to follow the following guidelines:

sumMass( items: Payload[] ): number Returns the sum of all items using each item's massKg property

Payload is an import from another typescript file that looks like

export interface Payload {
    massKg: number;
}

here is the code i have for my Rocket class that is supposed to accept items of type Payload array and give a number output. I keep getting this error

Rocket.ts(20,12): error TS2365: Operator '+=' cannot be applied to types 'number' and 'Payload'.

import { Payload } from './Payload';
 import { Astronaut } from './Astronaut';
 import { Cargo } from './Cargo';

export class Rocket implements Payload {
    name: string;
    massKg: number;
    totalCapacityKg: number;
    cargoItems: Cargo[] = [];
    astronauts: Astronaut[] = [];

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

    sumMass(items: Payload[]): number {
        let sum: number = 0;
         for(let i = 0; i < items.length; i++){
           sum += items[0];
         }
        return sum;

    }
}

let myRocket = new Rocket('rocket', 7);
console.log(myRocket.name);
console.log(myRocket.sumMass([]));

I'm just not sure how to use the interface as an array or how to go about constructing this method any longer. Any advice appreciated thank you!

Answer 1

It should be

   sum += items[i].massKg;

Your function doesnt appear to operate on any class properties so could exist entirely outside of your class. I would suggest using reduce to simplify this method further