Modify array element access to make it 1-based index

Question

I've run across a codewars exercise which I'm struggling with: https://www.codewars.com/kata/scraping-codewars-top-500-users/train/javascript

I want to be able to access an array as if was 1-indexed, instead of 0-indexed.

For example, if I have this array:

let a = [1, 2, 3, 4, 5]

I would like to do a[5] and get 5 as a result (instead of 4).

So far, I've come up with this:

Array.prototype.get = function(i, fallback) {
  return this[i-1] || fallback;
}

And with:

class BaseOneArray extends Array {
    constructor(...args) { 
        super(...args); 
    }
    get(i, fallback) {
        return this[i-1];
    }
}

However, both of these approaches only work when accessing the array like this: a.get(4) but not when doing it like this: a[4]

How could I make the [] operators from an array work as if the array had a 1-based index?

The array must have the same number of items, so I can't just add a fill value in the first position to move all the elements one place up.

Potentially relevant: https://stackoverflow.com/questions/1711357/how-would-you-overload-the-operator-in-javascript — OliverRadini, Aug 10 '18 at 12:24

Jonas Wilms · Accepted Answer · 2018-08-10T12:36:02.067

2

To influence property accesses you could use a proxy that increases every property access:

  array =  new Proxy(array, {
    get(target, prop, receiver) {
      if(!isNaN(+prop)) --prop;
      return Reflect.get(target, prop, receiver);
    },
    set(target, prop, value) {
      if(!isNaN(+prop)) --prop;
      return Reflect.set(target, prop, value);
    },
  });

By proxying the underlying array still stays zero based, just your "view" of it is changed so if the array is used somewhere else that doesnt get affected.

edited Aug 10 '18 at 12:36

answered Aug 10 '18 at 12:28

Jonas Wilms

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1

maybe you should check for integer values as well ... and for 32 bit ... and positive ... ;-) – Nina Scholz Aug 10 '18 at 13:01

void · Answer 2 · 2018-08-10T12:27:47.663

1

If you can modify the array then you can do something like this.

let a = [1, 2, 3, 4, 5]
a = [undefined, ...a];

console.log("a[5] is ", a[5]);
console.log("a[0] is ", a[0]); // Same as accessing any undefined index. See below
console.log("a[100] is ", a[100]);

edited Aug 10 '18 at 12:27

answered Aug 10 '18 at 12:25

void

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score 1 · Answer 3 · answered Aug 10 '18 at 12:36

The code test does not specify you need an array, it just says "Leaderboard#position[i] should return the ith ranked User(1 based index)". You should be able to simply use an object with numeric keys then:

const leaderboard = yourFetchedAndParsedLeaderboardDomElementArray
  .reduce((acc, row, index) => Object.assign(acc, {
    [index + 1]: {
      // get the following ones from `row` somehow:
      name: ...,
      clan: ...,
      author: ...
    }
  }), {});

You can use the object spreading syntax if available rather than Object.assign.

Modify array element access to make it 1-based index

3 Answers3