Custom JS Shuffle - Keep First

custom-first-shuffle.js

function customShuffle(x) {
  var y = x.slice(1, x.length);
  var j, t, i;
  for (i = y.length - 1; i > 0; i--) {
      j = Math.floor(Math.random() * (i + 1));
      t = y[i];
      y[i] = y[j];
      y[j] = t;
  }
  return [x[0]].concat(y);
}

Shuffles a JS array, leaving the first element in place.

Here's another way to do it

const customShuffle = (theArray) => [
  theArray[0],
  ...theArray.slice(1, -1)
    .map(n =>[Math.random(), n])
    .sort((a, b) => a[0] - b[0])
    .map(n => n[1])
]
customShuffle([1,2,3,4,5,6,7,8,9])