API / Js / Json

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(These docs cover all versions between v3 to v8 and are equivalent to the old BuckleScript docs before the rebrand)

Json

Provide utilities for JSON.

t

type t;

The JSON data structure.

kind

type kind('a) = | String: kind(Js_string.t) | Number: kind(float) | Object: kind(Js_dict.t(t)) | Array: kind(array(t)) | Boolean: kind(bool) | Null: kind(Js_types.null_val);

Underlying type of a JSON value.

tagged_t

type tagged_t = | JSONFalse | JSONTrue | JSONNull | JSONString(string) | JSONNumber(float) | JSONObject(Js_dict.t(t)) | JSONArray(array(t));

classify

let classify: t => tagged_t;

test

let test: ('a, kind('b)) => bool;

test(v, kind) returns true if v is of kind.

decodeString

let decodeString: t => option(Js_string.t);

decodeString(json) returns Some(s) if json is a string, None otherwise.

decodeNumber

let decodeNumber: t => option(float);

decodeNumber(json) returns Some(n) if json is a number, None otherwise.

decodeObject

let decodeObject: t => option(Js_dict.t(t));

decodeObject(json) returns Some(o) if json is an object, None otherwise.

decodeArray

let decodeArray: t => option(array(t));

decodeArray(json) returns Some(a) if json is an array, None otherwise.

decodeBoolean

let decodeBoolean: t => option(bool);

decodeBoolean(json) returns Some(b) if json is a boolean, None otherwise.

decodeNull

let decodeNull: t => option(Js_null.t('a));

decodeNull(json) returns Some(null) if json is a null, None otherwise.

null

let null: t;

null is the singleton null JSON value.

string

let string: string => t;

string(s) makes a JSON string of the string s.

number

let number: float => t;

number(n) makes a JSON number of the float n.

boolean

let boolean: bool => t;

boolean(b) makes a JSON boolean of the bool b.

object_

let object_: Js_dict.t(t) => t;

object_(dict) makes a JSON object of the Js.Dict.t dict.

array

let array: array(t) => t;

array_(a) makes a JSON array of the Js.Json.t array a.

stringArray

let stringArray: array(string) => t;

stringArray(a) makes a JSON array of the string array a.

numberArray

let numberArray: array(float) => t;

numberArray(a) makes a JSON array of the float array a.

booleanArray

let booleanArray: array(bool) => t;

booleanArray(a) makes a JSON array of the bool array a.

objectArray

let objectArray: array(Js_dict.t(t)) => t;

objectArray(a) makes a JSON array of the JsDict.tarraya`.

parseExn

let parseExn: string => t;

parseExn(s) parses the string s into a JSON data structure. Returns a JSON data structure. Raises SyntaxError if the given string is not a valid JSON. Note: SyntaxError is a JavaScript exception.

RE
/* parse a simple JSON string */ let json = try (Js.Json.parseExn({| "foo" |})) { | _ => failwith("Error parsing JSON string") }; switch (Js.Json.classify(json)) { | Js.Json.JSONString(value) => Js.log(value) | _ => failwith("Expected a string") };
RE
/* parse a complex JSON string */ let getIds = s => { let json = try (Js.Json.parseExn(s)) { | _ => failwith("Error parsing JSON string") }; switch (Js.Json.classify(json)) { | Js.Json.JSONObject(value) => /* In this branch, compiler infer value : Js.Json.t Js.Dict.t */ switch (Js.Dict.get(value, "ids")) { | Some(ids) => switch (Js.Json.classify(ids)) { | Js.Json.JSONArray(ids) => /* In this branch compiler infer ids : Js.Json.t array */ ids | _ => failwith("Expected an array") } | None => failwith("Expected an `ids` property") } | _ => failwith("Expected an object") }; }; /* prints `1, 2, 3` */ Js.log(getIds({| { "ids" : [1, 2, 3 ] } |}));

stringify

let stringify: t => string;

stringify(json) formats the JSON data structure as a string. Returns the string representation of a given JSON data structure.

RE
/* Creates and stringifies a simple JS object */ { let dict = Js.Dict.empty(); Js.Dict.set(dict, "name", Js.Json.string("John Doe")); Js.Dict.set(dict, "age", Js.Json.number(30.0)); Js.Dict.set( dict, "likes", Js.Json.stringArray([|"bucklescript", "ocaml", "js"|]), ); Js.log(Js.Json.stringify(Js.Json.object_(dict))); };

stringifyWithSpace

let stringifyWithSpace: (t, int) => string;

stringify(json) formats the JSON data structure as a string. Returns the string representation of a given JSON data structure with spacing.

RE
/* Creates and stringifies a simple JS object with spacing */ { let dict = Js.Dict.empty(); Js.Dict.set(dict, "name", Js.Json.string("John Doe")); Js.Dict.set(dict, "age", Js.Json.number(30.0)); Js.Dict.set( dict, "likes", Js.Json.stringArray([|"bucklescript", "ocaml", "js"|]), ); Js.log(Js.Json.stringifyWithSpace(Js.Json.object_(dict), 2)); };

stringifyAny

let stringifyAny: 'a => option(string);

stringifyAny(value) formats any value into a JSON string.

RE
/* prints `["foo", "bar"]` */ Js.log(Js.Json.stringifyAny([|"foo", "bar"|]));