A map is a collection of key-value pairs, with unique keys.
An iterable is a sequence of values.
An array is a collection of values, stored contiguously.
Entries is a list of key-value pairs, with unique keys.
A set is a collection of unique values.
An object is a collection of properties, with associated values.
Lists is a pair of key list and value list, with unique keys.
Finds key of first entry passing a test.
Scans from left, until a test passes.
Finds first value passing a test.