changing array and obj without modify original one

changingArrayAndObject.js

// remove index-1 position component of array without modify the origin array
list = [1, 2, 3, 4, 5]
const removeCounter = (list, index) => {
  return [
    ...list.slice(0, index),
    ...list.slice(index + 1)
  ];
}
removerCounter(list, 3); //[1, 2, 4, 5];

//==================================================================

//===== add an counter in an array=============
const addCounter = (list) => {
  return list.concat([0]);
};
//===== ES6 =========================
const addCounter = (list) => {
  return [...list, 0];
};

//========================== Modify Object ES6 way ======================
const toggleTodo = (todo) => {
  return Object.assign({}, todo, {
    completed: !todo.completed
  });
};

// ============================= ES7 way ===================================
const toggleTodo = (todo) => {
  return {
    ...todo,
    completed: !todo.completed
  };
};

https://egghead.io/lessons/react-redux-avoiding-object-mutations-with-object-assign-and-spread