A "real" array in JS. Not really.

real-array.js

class RealArray extends Array {
  constructor(length) {
    if (!Number.isInteger(length) || length < 0) {
      throw new Error('RealArray requires a positive integer length')
    }
    function boundsCheck(index) {
      if (index in Array.prototype) {
        throw new RangeError('RealArray does not have ' + index)
      }
      if (parseInt(index, 10) !== parseFloat(index, 10)) {
        throw new RangeError('index must be an integer')
      }
      if (index < 0 || index >= length) {
        throw new RangeError('index out of bounds of RealArray')
      }
    }
    super(length)
    Object.defineProperty(this, 'length', {
      value: length,
      writable: false,
      configurable: false
    })
    this.__proto__ = new Proxy(this.fill(null), {
      has() {
        return false
      },
      getPrototypeOf() {
        return Array.prototype
      },
      get(array, index) {
        boundsCheck(index)
        return array[index]
      },
      set(array, index, value) {
        boundsCheck(index)
        return (array[index] = value)
      },
    })
    Object.preventExtensions(this)
  }
}