find, some, every

Asking questions of an array

Three more methods take an arrow that answers true or false, but instead of building arrays they answer questions:

• find(test) → the first item that passes, or undefined if none do.
• some(test) → true if at least one item passes (Python's any).
• every(test) → true if all items pass (Python's all).

They shine on arrays of objects, which is how real data usually arrives:

const users = [
  { name: "Ada", age: 36 },
  { name: "Alan", age: 41 }
];

const alan = users.find(u => u.name === "Alan");   // the whole object

find hands you the object itself, so alan.age is 41. For simple membership checks on plain values, includes from lesson 4-2 is still the shortest tool.