immutable-patterns.js

/*
 * Immutable data patterns without Immutable.js
 */

// 1. Objects
const a = { name: 'Alice', age: 20, email: 'alice@example.com' };

// updating property
const b = { ...x, age: 21 };
b; //=> { name: 'Alice', age: 21, email: 'alice@example.com' }

// deleting property
const { email: deleted, ...c } = a;
c; //=> { name: 'Alice', age: 20 }

// 2. Arrays
const arr = [1, 2, 3, 4];

// pushing value
const arr2 = x.concat([5]);
arr2; //=> [1, 2, 3, 4, 5]

// unshifting value
const arr3 = [5].concat(arr);
arr3; //=> [5, 1, 2, 3, 4]

// removing from front
const [front, ...arr4] = arr;
arr4; //=> [2, 3, 4]

// removing from back
const arr5 = [].concat(arr).splice(0, 3);
arr5; //=> [1, 2, 3]

// removing from middle (LOL)
const arr6 = [].concat([].concat(arr).splice(0, 1)).concat([].concat(arr).splice(2, 2));
arr6; //=> [1, 3, 4]

.slice(1)
.slice(0, -2)