Master array methods (map, filter, reduce), string operations, and common algorithms like searching and sorting. Arrays are O(1) access, O(n) insertion/deletion.

• Array methods (map, filter, reduce)
• String operations
• Common algorithms like searching
• Sorting

const arr = [1, 2, 3, 4, 5];
const doubled = arr.map(x => x * 2);
console.log(doubled);

const evens = arr.filter(x => x % 2 === 0);
console.log(evens);
// ...

• map doubles values
• filter gets evens

• map: transform each element; filter: keep elements that pass test; reduce: combine to single value
• String methods: slice, substring, indexOf, split, join
• Array search: indexOf is O(n); Set lookup is O(1)

Master array methods (map, filter, reduce), string operations, and common algorithms like searching and sorting. Arrays are O(1) access, O(n) insertion/deletion.

• Array methods (map, filter, reduce)
• String operations
• Common algorithms like searching
• Sorting

const arr = [1, 2, 3, 4, 5];
const doubled = arr.map(x => x * 2);
console.log(doubled);

const evens = arr.filter(x => x % 2 === 0);
console.log(evens);
// ...

• map doubles values
• filter gets evens

• map: transform each element; filter: keep elements that pass test; reduce: combine to single value
• String methods: slice, substring, indexOf, split, join
• Array search: indexOf is O(n); Set lookup is O(1)