How to set the value of the elements of the array to their position in the array in JavaScript

Question

I have an array of objects such as:

let array = [{ position:0 },{ position:1 },{ position:2 }]

I wish that each object should store it's own position and update it when it's position is changed.

I'm using - array.splice(); to delete an object and then using this loop to calculate their positions again -

for(let i = 0, length1 = array.length; i < length1; i++){ array[i].position=i; }

But I want this to be done automatically without the loop Is there any way to achieve this in js.

Answer 1

....and update it when it's position is changed

That's the tricky bit, you'd either need to wrap a Proxy around the array and update the positions when things change:

let array = [{position: 0},{position: 1},{position: 2}];
function updateIndexes(array) {
    array.forEach((entry, index) => {
        entry.position = index;
    });
}
let parray = new Proxy(array, {
    defineProperty(target, key, descriptor) {
        const result = Reflect.defineProperty(target, key, descriptor);
        updateIndexes(target);
        return result;
    },
    set(target, key, value) {
        const result = Reflect.set(target, key, value);
        updateIndexes(target);
        return result;
    }
});

let second = parray[1];
console.log(second.position); // 1
parray.splice(0, 1);
console.log(second.position); // 0

...or make the position an accessor property that searches for the object in the array and returns its current position, which means creating the accessor where it closes over the array:

let array = [
    {
        get position() {
            return array.indexOf(this);
        }
    },
    {
        get position() {
            return array.indexOf(this);
        }
    },
    {
        get position() {
            return array.indexOf(this);
        }
    }
];

let second = array[1];
console.log(second.position); // 1
array.splice(0, 1);
console.log(second.position); // 0