AI solution for JavaScript Coding Question on BFE.dev
88. support negative Array index in JavaScript

One possible solution:

function wrap(arr) {
  return new Proxy(arr, {
    get(target, prop) {
      if (typeof prop === 'string' && /^[0-9]+$/.test(prop)) {
        prop = parseInt(prop);
      }
      if (typeof prop === 'number' && prop < 0) {
        prop += target.length;
      }
      return target[prop];
    },
    set(target, prop, value) {
      if (typeof prop === 'string' && /^[0-9]+$/.test(prop)) {
        prop = parseInt(prop);
      }
      if (typeof prop === 'number' && prop < 0) {
        prop += target.length;
      }
      target[prop] = value;
      return true;
    }
  });
}

This function creates a Proxy object around the original array arr, which intercepts all property access and assignment. If the property name is a string that can be converted to a non-negative integer, it is converted to a number. If the number is negative, it is wrapped around to the corresponding positive index by adding the length of the array. All other property access and assignment are delegated to the original array.

With this wrapper function, you can use negative array index in JavaScript just like in Python.