pure examples 1

pure`.js

// pure
const addOne = num => num + 1;

//impure: modifies input variable
const addOneImpure = num => num++;

//pure
const addOneToAll = arr => arr.map(addOne);

//impure: modifies input array
const addOneToAllImpure = arr => {
  for (let i = 0; i < arr.length; i++) {
    addOneImpure(arr[i]);
  }
}

//pure
const addWheels = (obj, num) => Object.assign({}, obj, {wheels: num});

const noWheelTruck = {type: 'truck'};

const fourWheelTruck = addWheels(noWheelTruck, 4) //=> {type: 'truck', wheels: 4}
console.log(noWheelTruck) // {type: 'truck'} original object unchanged

//impure
const addWheelsImpure = (obj, num) => {obj['wheels'] = num};

const noWheelCar = {type: 'car'};

const fourWheelCar = addWheelsImpure(noWheelCar, 4); //=>{type: 'car', wheels: 4}
console.log(noWheelCar) //{ type: 'car', wheels: 4 } MUTATED!

I think addOneImpure will not do anything, it should be ++num, but even if you did that, the number is a primitive thus it will not modify the passed variable.