1. Know it's an array or not
const points = [23, 3, 89, 98, 40]
// Before 😏
console.log(points.length)
// it returns true
// After 👌
console.log(Array.isArray(points))
// it returns true
2. Get last element of an array
const points = [23, 3, 89, 98, 40]
// Before 😏
console.log(points[points.length - 1])
// it returns 40
// After 👌
console.log(points.at(-1))
// it returns 40
3. Count occurrences in an array
const occurencies = (arr) =>
arr.reduce((a, v) => {
a[v] = a[v] ? a[v] + 1 : 1;
return a;
}, {});
occurencies(['a', 'b', 'a', 'c', 'a', 'a', 'b'])
// {a: 4, b: 2, c: 1}
occurencies([...'soccer'])
// {s: 1, o: 1, c: 2, r: 1}