ArrayList Polyfill Shims for JS Arrays

ArrayList_Shims.js

// ArrayList Polyfill Shims for JS Arrays (v1.0.1)
// GoToLoop (2020/Nov/05)
// https://Gist.GitHub.com/GoToLoop/a74c5780667f2610097cfc007e53a559

"use strict";

// Add some useful Java list's methods to JS arrays as polyfills:
Object.defineProperties(Array.prototype, {
  size: {
    value() { // polyfill hack to add method size() to JS arrays
      return this.length; // return array's current length
    }
  },

  isEmpty: {
    value() { // polyfill hack to add method isEmpty() to JS arrays
      return !this.length; // return true if length is 0
    }
  },

  clear: {
    value() { // polyfill hack to add method clear() to JS arrays
      return this.length = 0, this; // remove all elements
    }
  },

  get: {
    value(idx) { // polyfill hack to add method get() to JS arrays
      return this[idx]; // so its indices can be accessed like a Java list
    }
  },

  set: {
    value(idx, elem) { // polyfill hack to add method set() to JS arrays
      return this[idx] = elem; // replace elem at specified index
    }
  },

  add: {
    value() { // polyfill hack to add method add() to JS arrays
      arguments.length > 1?
        this.splice(arguments[0], 0, arguments[1]) : // add at specified index
        this.push(arguments[0]); // append to array's tail
      return this;
    }
  },

  addAll: {
    value() { // polyfill hack to add method addAll() to JS arrays
      arguments.length > 1?
        this.splice(arguments[0], 0, ...arguments[1]) : // add all at index
        this.push(...arguments[0]); // append all items to array's tail
      return this;
    }
  },

  remove: {
    value(val) { // polyfill hack to add method remove() to JS arrays
      // idx is val if its type is number, otherwise find its index:
      const idx = typeof val == 'number'? val : this.indexOf(val);

      // Remove & return the element at index idx or return false:
      return ~idx? this.splice(idx, 1)[0] : false;
    }
  },

  toArray: {
    value() { // polyfill hack to add method toArray() to JS arrays
      if (!arguments.length)  return this.slice(); // returns array clone

      const [ arr ] = arguments, arrLen = arr.length, thisLen = this.length;

      if (arrLen < thisLen)  return this.slice(); // returns clone if too small
      else if (arrLen > thisLen)  arr[thisLen] = null; // marks the array end

      for (var i = 0; i < thisLen; arr[i] = this[i++]); // array transfer
      return arr; // returns passed array filled w/ this array
    }
  },

  clone: { // method clone() is like invoking slice() w/ no arguments
    value: Array.prototype.slice
  }
});