Objects

Objects store data as key-value pairs. Looking up a value by its key is fast, which makes objects (and Map) great for counting things or quick lookups.

const user = { name: "Daniel", age: 20 }

user.name             // "Daniel"
user["age"]           // 20
user.city = "Dallas"  // add a key
delete user.age       // remove a key
"name" in user        // true

Object.keys(user)     // ["name", "city"]
Object.entries(user)  // [["name","Daniel"], ["city","Dallas"]]

// Count letters
const counts: Record<string, number> = {}
for (const ch of "hello") counts[ch] = (counts[ch] || 0) + 1
// { h: 1, e: 1, l: 2, o: 1 }