Simple JavaScript Array Moves
Array moves are usually done with cumbersome syntax. But by using certian syntax, they can be made easier. Firstly to shift contents from the beggining of an array to the end and vice versa, push and unshift can be combined with pop and shift:
// Shift first to end const arr1 = [4,1,2,3]; arr1.push(arr1.shift()); console.log(arr1); // [ 1, 2, 3, 4 ] // Shift last to start const arr2 = [2,3,4,1]; arr2.unshift(arr2.pop()); console.log(arr2); // [ 1, 2, 3, 4 ]
The general form of pop and shift is splice which takes 3 arguments: The place to start an operation, the number of elements to delete after and then the rest of the arguments are the elements to insert. For example:
// Shift 2nd to 4rd (Get and remove 2nd, move to first) const arr3 = [1,4,2,3,5]; arr3.splice(3, 0, arr3.splice(1, 1)[0]); console.log(arr3); // [ 1, 2, 3, 4, 5 ]
This can be generalized to support an easier to read arrayMove function:
function arrayMove(arr, from, to) { // Slice makes it non-mutable arr = arr.slice(); arr.slice().splice(to, 0, arr.splice(from, 1)[0]); return arr; } const arr4 = [1,4,2,3,5]; console.log(arrayMove(arr4, 1, 3)); // [ 1, 2, 3, 4, 5 ]
slice is normally used to take a part of an array, but with no arguments it just gives the whole array. Making it an easier way to clone the array (The elements themselves are shared between arrays though if they are objects).
Finally, splice can be used for more advanced operations like moving multiple items at once:
function arrayMove2(arr, from, to, amount = 1) { // Slice makes it non-mutable arr = arr.slice(); arr.splice.apply(arr, [to, 0].concat(arr.splice(from, amount))); return arr; } const arr7 = [1,4,5,2,3]; console.log(arrayMove2(arr7, 1, 3, 2)); // [ 1, 2, 3, 4, 5 ]
Note that slice takes the elements to insert as arguments. splice returns an array of what was removed, so instead apply is used to send the arguments in as a list, meaning the elements to insert can simply be appended to that list.
Github Location https://github.com/Jacob-Friesen/obscurejs/blob/master/2017/arrayMove.js
prguitarman
origamiaround
snowghoul
vaporwave
blakekathryn
stormborns
izzy806
