Move item in array to last position

Moving the first element of an array to the end of the same array

    var a = [5,1,2,3,4];
    a.push(a.shift());
    console.log(a); // [1,2,3,4,5]

or this way

    var a = [5,1,2,3,4];
    var b = a.shift();
    a[a.length] = b;
    console.log(a); // [1,2,3,4,5]

Moving any element of an array to any position in the same array

    // move element '5' (index = 2) to the end (index = 4)
    var a = [1, 2, 5, 4, 3];
    a.splice(4,0,a.splice(2,1)[0]);
    console.log(a); // [1, 2, 4, 3, 5]

or it could be converted to a prototype as well, like this where x represents the current position of element while y represents the new position in array

var a = [1, 2, 5, 4, 3];
Array.prototype.move = function(x, y){
      this.splice(y, 0, this.splice(x, 1)[0]);
      return this;
    };
    
    a.move(2,4);
    console.log(a); // ["1", "2", "4", "3", "5"]

Answer to the @jkalandarov comment

function moveToTheEnd(arr, word){
  arr.map((elem, index) => {
    if(elem.toLowerCase() === word.toLowerCase()){
      arr.splice(index, 1);
      arr.push(elem);
    }
  })
  return arr;
}
console.log(moveToTheEnd(["Banana", "Orange", "Apple", "Mango", "Lemon"],"Orange"));

to move an element (of which you know the index) to the end of an array, do this:

array.push(array.splice(index, 1)[0]);

If you don't have the index, and only the element, then do this:

array.push(array.splice(array.indexOf(element), 1)[0]);

Example:

    var arr = [1, 2, 6, 3, 4, 5];
    arr.push(arr.splice(arr.indexOf(6), 1)[0]);
    console.log(arr); // [1, 2, 3, 4, 5, 6]

NOTE:

this only works with Arrays (created with the [ ... ] syntax or Array()) not with Objects (created with the { ... } syntax or Object())