Reference · Maps

has

has(map | null, any) -> bool

What it does

Whether a map has an entry under a key: true or false. The key is turned into text first, as all map keys are. An entry whose value is null counts as present, which is what tells has apart from get(m, k) != null.

Examples

let user = { name: "Ann", email: null }print(has(user, "name"), has(user, "phone"))print(has(user, "email"), get(user, "email") != null)

true falsetrue false

Edge cases

• Keys are text: has(m, 5) finds "5".
• null as the map is an empty map: has(null, k) is false.
• contains(m, k) on a map asks the same question.
• An error value as the key is given back, neither true nor false.

let m = { "5": "five" }print(has(m, 5), has(m, "5"), has(m, 6))print(has(null, "a"), has({}, ""))print(contains(m, "5"))print(has(m, int("q")))

true true falsefalse falsetrueerr("not an int: \"q\"")

Errors

A map that is not a map or null is a runtime error, not an error value. For a list, contains looks for an item.

print(has(3, "a"))

line 1: `has` expects a map as argument 1, got int

Chaining

let m = { a: 1, b: 2 }print(m | has("a"))print(["a", "x", "b"] | filter((k) => has(m, k)))

true["a", "b"]

See also

get, keys, contains, set

Edit this page on GitHub · every example's output was made by running it (tools/refcheck.mjs) · questions on Discord or r/quillo