プロキシ - JavaScript の課題

/**
 * @param {Array} arr 
 */

function withNegativeIndex(arr) {
  return new Proxy(arr, {
    get(target, property, receiver) {
      const index = Number(property);

      if (index < 0) {
        property = target.length + index;
      }

      return Reflect.get(target, property, receiver);
    }
  });
}

// Usage example
const fruits = ["apple", "banana", "orange"];
const proxiedFruits = withNegativeIndex(fruits);

console.log(proxiedFruits[-1]); // => 'orange'
console.log(proxiedFruits[-2]); // => 'banana'
console.log(proxiedFruits[-3]); // => 'apple'
console.log(proxiedFruits[0]);  // => 'apple'
console.log(proxiedFruits[1]);  // => 'banana'
console.log(proxiedFruits[2]);  // => 'orange'