arguments

function func1(a, b, c) {
  console.log(arguments[0]);
  // Expected output: 1

  console.log(arguments[1]);
  // Expected output: 2

  console.log(arguments[2]);
  // Expected output: 3
}

func1(1, 2, 3);

arguments[0];
arguments[1];
arguments[2];

arguments[1] = "new value";

var args = Array.prototype.slice.call(arguments);
var args = [].slice.call(arguments);

// ES2015
const args = Array.from(arguments);
const args = [...arguments];

var args = Array.from(arguments);
var args = [...arguments];

function myConcat(separator) {
  var args = Array.prototype.slice.call(arguments, 1);
  return args.join(separator);
}

//  "red, orange, blue"
myConcat(", ", "red", "orange", "blue");

//  "elephant; giraffe; lion; cheetah"
myConcat("; ", "elephant", "giraffe", "lion", "cheetah");

//  "sage. basil. oregano. pepper. parsley"
myConcat(". ", "sage", "basil", "oregano", "pepper", "parsley");

function list(type) {
  var result = "<" + type + "l><li>";
  var args = Array.prototype.slice.call(arguments, 1);
  result += args.join("</li><li>");
  result += "</li></" + type + "l>"; //  

  return result;
}

var listHTML = list("u", "One", "Two", "Three");

/* listHTML:

"<ul><li>One</li><li>Two</li><li>Three</li></ul>"

*/

function foo(...args) {
  return arguments;
}
foo(1, 2, 3); // { "0": 1, "1": 2, "2": 3 }

function bar(a = 1) {
  arguments[0] = 100;
  return a;
}
bar(10); // 10

function zoo(a) {
  arguments[0] = 100;
  return a;
}
zoo(10); // 100

function func(a, b) {
  arguments[0] = 90;
  arguments[1] = 99;
  console.log(a + " " + b);
}

func(1, 2); //90, 99

function func(a, b) {
  a = 9;
  b = 99;
  console.log(arguments[0] + " " + arguments[1]);
}

func(3, 4); //9, 99

function func(a, b, c = 9) {
  arguments[0] = 99;
  arguments[1] = 98;
  console.log(a + " " + b);
}

func(3, 4); //3, 4