Nodejs Utililty Methods Array Move Down

Array.prototype.moveDown = function(element, offset) 
    var index = this.indexOf(element); 
    var newPos = index + (offset || 1);
    if(index === -1) { throw new Error("Element not found in array"); }
    if(newPos >= this.length) { newPos = this.length; }
    this.splice(index, 1);
    this.splice(newPos,0,element);
};
...

Array.prototype.moveDown = function(value, by) {
  var index = this.indexOf(value);
  if (index === -1) {
    throw new Error('Item not found');
  var newPos = index + (pos || 1);
  if (newPos >= this.length) {
    newPos = this.length;
  this.splice(index, 1);
  this.splice(newPos, 0, value);

Array.prototype.moveDown = function(value, by) {
    var index = this.indexOf(value),
        newPos = index + (by || 1);
    if(index === -1)
        throw new Error("Element not found in array");
    if(newPos >= this.length)
        newPos = this.length;
    this.splice(index, 1);
    this.splice(newPos,0,value);
...

Array.prototype.moveElement = function (index, delta) {
    var index2, temp_item;
    if (index < 0 || index >= this.length) {
        return false;
    index2 = index + delta;
    if (index2 < 0 || index2 >= this.length || index2 == index) {
        return false;
    temp_item = this[index2];
    this[index2] = this[index];
    this[index] = temp_item;
    return true;
};
Array.prototype.getPageData = function(data, pageSize, currentPageNo)
    var start = currentPageNo * pageSize,
        end = (currentPageNo * pageSize + pageSize) > data.length
                ? data.length
                : (pageSize * pageSize + pageSize);
    return data.slice(start, end);
};