Javascript Arrays (What to learn

https://www.w3schools.com/js/js_arrays.asp

Structure of Arrays
Iteration on arrays

Array methods : https://www.w3schools.com/js/js_array_methods.asp

concat vs join
push
splice/shift/pop
sorting: https://www.w3schools.com/js/js_array_sort.asp
shuffling

Following is generic shuffling algorithm in java-script for all arrays

function shuffle(array) {
  var currentIndex = array.length, temporaryValue, randomIndex;

  // While there remain elements to shuffle...
  while (0 !== currentIndex) {

    // Pick a remaining element...
    randomIndex = Math.floor(Math.random() * currentIndex);
    currentIndex -= 1;

    // And swap it with the current element.
    temporaryValue = array[currentIndex];
    array[currentIndex] = array[randomIndex];
    array[randomIndex] = temporaryValue;
  }

  return array;
}