Dict

RE
let ages = Js.Dict.fromList(
  [("Maria", 30), ("Vinh", 22), ("Fred", 49)]
);

t

type t('a);

Dictionary type (ie an '{ }' JS object). However it is restricted to hold a single type; therefore values must have the same type. This Dictionary type is mostly used with the Js_json.t type.

key

type key = string;

The type for dictionary keys. This means that dictionaries must use strings as their keys.

get

let get: (t('a), key) => option('a);

Js.Dict.get(key) returns None if the key is not found in the dictionary, Some(value) otherwise.

RE
Js.Dict.get(ages, "Vinh") == Some(22);
Js.Dict.get(ages, "Paul") == None;

unsafeGet

let unsafeGet: (t('a), key) => 'a;

Js.Dict.unsafeGet(key) returns the value if the key exists, otherwise an undefined value is returned. Use this only when you are sure the key exists (i.e. when having used the keys() function to check that the key is valid).

RE
Js.Dict.unsafeGet(ages, "Fred") == 49;
Js.Dict.unsafeGet(ages, "Paul"); // returns undefined

set

let set: (t('a), key, 'a) => unit;

Js.Dict.set(dict, key, value) sets the key/value in the dictionary dict. If the key does not exist, and entry will be created for it. This function modifies the original dictionary.

RE
Js.Dict.set(ages, "Maria", 31)
Js.log(ages ==
  Js.Dict.fromList([("Maria", 31), ("Vinh", 22), ("Fred", 49)]));

Js.Dict.set(ages, "David", 66)
Js.log(ages ==
  Js.Dict.fromList([("Maria", 31), ("Vinh", 22), ("Fred", 49), ("David", 66)]));

keys

let keys: t('a) => array(string);

Returns all the keys in the dictionary dict.

RE
Js.Dict.keys(ages) == [|"Maria", "Vinh", "Fred"|];

empty

let empty: unit => t('a);

Returns an empty dictionary.

unsafeDeleteKey

let unsafeDeleteKey: (. t(string), string) => unit;

Experimental internal function

entries

let entries: t('a) => array((key, 'a));

Returns an array of key/value pairs in the given dictionary (ES2017).

RE
Js.Dict.entries(ages) == [|("Maria", 30), ("Vinh", 22), ("Fred", 49)|]

values

let values: t('a) => array('a);

Returns the values in the given dictionary (ES2017).

RE
Js.Dict.values(ages) == [|30, 22, 49|]

fromList

let fromList: list((key, 'a)) => t('a);

Creates a new dictionary containing each (key, value) pair in its list argument.

RE
let capitals = Js.Dict.fromList([("Japan", "Tokyo"), ("France", "Paris"), ("Egypt", "Cairo")]);

fromArray

let fromArray: array((key, 'a)) => t('a);

Creates a new dictionary containing each (key, value) pair in its array argument.

RE
let capitals2 = Js.Dict.fromArray([|("Germany", "Berlin"), ("Burkina Faso", "Ouagadougou")|]);

map

let map: ((. 'a) => 'b, t('a)) => t('b);

map(f, dict) maps dict to a new dictionary with the same keys, using the function f to map each value.

RE
let prices = Js.Dict.fromList([("pen", 1.00), ("book", 5.00), ("stapler", 7.00)]);

let discount = (. price) => {price *. 0.90};
let salePrices = Js.Dict.map(discount, prices);

salePrices == Js.Dict.fromList([("pen", 0.90), ("book", 4.50), ("stapler", 6.30)]);