Reference · Maps

keys

keys(map | null) -> list

What it does

The keys of a map, as a list of strings, in the order the entries were added. A map's keys are always text, so a key that was set with a number comes back as its text. null counts as an empty map and gives [].

Examples

let user = { name: "Ann", age: 41, admin: false }print(keys(user))print(keys({ "x y": 1, "2": 2 }))

["name", "age", "admin"]["x y", "2"]

Edge cases

• Order is insertion order, not sorted: sort the list when an order is wanted. It is the same in the browser, keys that look like numbers included: keys({ b: 1, "1": 2 }) is ["b", "1"] on both sides, where a JavaScript object lists "1" first.
• set on a key that is already there keeps its place; remove and set again puts it at the end.
• An empty map and null both give [].
• len(keys(m)) is len(m).

let m = { b: 2, a: 1, c: 3 }print(keys(m), keys(m) | sort)print(keys(set(m, "a", 10)), keys(set(remove(m, "a"), "a", 10)))print(keys({}), keys(null))print(len(keys(m)), len(m))print(keys({ b: 1, "1": 2, a: 3, "0": 4 }))

["b", "a", "c"] ["a", "b", "c"]["b", "a", "c"] ["b", "c", "a"][] []3 3["b", "1", "a", "0"]

Errors

A list, a string or a number is a runtime error, not an error value: keys takes a map or null only. A list has no keys; enumerate gives its positions.

print(keys([1, 2]))

line 1: `keys` expects a map as argument 1, got list

Chaining

In a pipeline the map comes first. There is no entries: for [k, v] in m walks a map directly.

print({ b: 1, a: 2 } | keys | map(upper))for [k, v] in { a: 1, b: 2 } { print(k, v) }

["B", "A"]a 1b 2

See also

values, has, get, len, sort

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