FP in JS 3

fp_js_3.js

// A list of fruit, and their price
const fruit = [
  {name: 'banana', price: 5},
  {name: 'apple', price: 3},
  {name: 'pear', price: 7}
];

// Now we want to increase the price of all fruit
// Let's do this using a for loop
// NOTE: We're also mutating state here,
// which as you know can be dangerous
for (f of fruit) {
  f.price = f.price + 5;
}

// Instead, let's use map()
const moreExpensiveFruit = fruit
  .map(f => {
    return { ...f, price: f.price + 5 }
  });

// Now we're using functional programming!
// 1. We're not mutating fruit, instead we're copying data with the spread operatator `...`
// 2. map() returns a new list, so the fruit list is still unchanged