Using the rest operator to pass in a variable amount of arguments

Video

JS

// adding to an array
someBits = [ "bit two", "bit three"];
someMoreBits = [ "bit one", ...someBits, "bit four"]; // this shows how the operator can be used to insert the elements of the someBits array into this array, without the operator it will add the full array
console.log("----- [someMoreBits] -----");
console.log(someMoreBits);

someMoreBitsArray = [ "bit one", someBits, "bit four"]; // this array will have the someBits nested array rather than the elements.
console.log("----- [someMoreBitsArray] -----");
console.log(someMoreBitsArray);

// using for function
function add_nums(x,y,z) {
  console.log(x+y+z);
}

// use function manually
console.log("----- [use add_nums function manually] -----");
add_nums(1,2,3);
args = [1,2,3];

// use function with spread operator
console.log("----- [use add_nums function with args array] -----");
add_nums(...args);

// concatonate arrays
console.log("----- [concatonate (join/merge) arrays ] -----");
array_one = [1,2,3];
array_two = [4,5,6];
array_three = array_one.concat(array_two); // using the concat function
array_four = [...array_one, ...array_two]; // using spread
console.log(array_three);
console.log(array_four);

// REST: passing in multiple elements
function multirest(multi, ...args) {
    return args.map(function(element) {
        return multi * element;
    });
}
console.log("----- [ using rest to pass in multiple element and a multiplier ] -----");
var multi_array = multirest(2, 3, 4, 5);
console.log(multi_array);

function run_function(...args) {
  //const nums.map(args);
  result = args.length;
  // const nums = args.map(); // how to use map function? -- https://www.w3schools.com/jsref/jsref_map.asp
  write_result(result);
  return result;
}

// this is a common function just to write the content into the result div
function write_result(result) {
  var result_html = document.getElementById("result");
  result_html.innerHTML = result;
}

HTML

<div id='result' class='mb-3 alert alert-primary'>..</div>
<button onclick='run_function(1,2,3,4,5,6,7);' class='btn btn-primary mb-1'>Run Function</button>

Working Result

Test Result Below