checkProp

Given a predicate function and a prop string, this curried function will then take an object to inspect by calling the property and passing it to the predicate.

Summon prop on obj, pass it to a provided predicate function and return a masked boolean.

const checkProp = (predicate, prop) => (obj) => !!predicate(obj[prop]);

const lengthIs4 = checkProp((l) => l === 4, "length");
lengthIs4([]); // false
lengthIs4([1, 2, 3, 4]); // true
lengthIs4(new Set([1, 2, 3, 4])); // false (Set uses Size, not length)

const session = { user: {} };
const validUserSession = checkProp((u) => u.active && !u.disabled, "user");

validUserSession(session); // false

session.user.active = true;
validUserSession(session); // true

const noLength = checkProp((l) => l === undefined, "length");
noLength([]); // false
noLength({}); // true
noLength(new Set()); // true