function shuffle(array) {
  const curIdx = array.length;

  // While there remain elements to shuffle...
  while (0 !== cur_idx) {
    // Pick a remaining element...
    const randIdx = Math.floor(Math.random() * curIdx);
    curIdx -= 1;

    // And swap it with the current element.
    const originalIdx = array[curIdx];
    array[curIdx] = array[randIdx];
    array[randIdx] = originalIdx;
  }
  return array;
}

// Usage of shuffle
const arr = [1, 2, 3, 4, 5, 6];
arr = shuffle(arr);
console.log(arr);

// shorter
function shuffle(array) {
    for (let i = array.length - 1; i > 0; i--) {
        var j = Math.floor(Math.random() * (i + 1));
        var originalIdx = array[i];
        array[i] = array[j];
        array[j] = originalIdx;
    }
}

//es6
function shuffle_array(array) {
    for (let i = array.length - 1; i > 0; i--) {
        const j = Math.floor(Math.random() * (i + 1));
        [array[i], array[j]] = [array[j], array[i]];
    }
}