Ruby Array Methods in Javascript

array.js

/*** Custom RArray class ***/

class RArray extends Array {

  // Returns an array containing the items for which the given closure is not true.
  reject (callback) {
    return this.filter((val) => {
      return !callback(val);
    });
  }
  
  // Returns an array containing all elements of array for which the given closure returns a true value.
  select (callback) {
    return this.filter(callback);
  }
  
  //Invokes the given closure once for each element of self.
  collect (callback) {
    return this.map(callback);
  }
  
  // Same as forEach, but passes the index of the element instead of the element itself.
  eachIndex (callback) {
    return this.forEach((value, index) => {
      callback(index);
    });
  }
  
  // Returns true if self contains no elements.
  empty () {
    return this.length === 0;
  }
  
  // Returns the first element, or the first n elements, of the array. If the array is empty, the first form returns null, and the second form returns an empty array.
  first (n) {
    if (this.length === 0 && !n) return null;
    return this.slice(0, n || 1);
  }
  
  // Returns the last element, or the last n elements, of the array. If the array is empty, the first form returns null, and the second form returns an empty array.
  last (n) {
    if (this.length === 0 && !n) return null;
    return this.slice(-n || -1);
  }
  
  // Returns an array by removing duplicate values in self.
  uniq () {
    return this.filter((value, index, self) => self.indexOf(value) === index);
  }
}


/*** Through Prototype Polution ***/

// Returns an array containing the items for which the given closure is not true.
Array.prototype.reject = function (callback) {
	return this.filter((val) => {
		return !callback(val);
	})
}

// Returns an array containing all elements of array for which the given closure returns a true value.
Array.prototype.select = function (callback) {
	return this.filter(callback);
}

//Invokes the given closure once for each element of self.
Array.prototype.collect = function (callback) {
	return this.map(callback);
}
// Same as forEach, but passes the index of the element instead of the element itself.
Array.prototype.eachIndex = function (callback) {
	return this.forEach((value, index) {
		callback(index);
	});
}

// Returns true if self contains no elements.
Array.prototype.empty = function () {
	return this.length === 0;
}

// Returns the first element, or the first n elements, of the array. If the array is empty, the first form returns null, and the second form returns an empty array.
Array.prototype.first = function (n) {
	if (this.length === 0 && !n) return null;
	return this.slice(0, n || 1);
}

// Returns the last element, or the last n elements, of the array. If the array is empty, the first form returns null, and the second form returns an empty array.
Array.prototype.last = function (n) {
	if (this.length === 0 && !n) return null;
	return this.slice(-n || -1);
}

// Returns an array by removing duplicate values in self.
Array.prototype.uniq = function () {
	return this.filter((value, index, self) => self.indexOf(value) === index);
}