Json

Efficient JSON encoding using JavaScript API

see MDN

The JSON data structure

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

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

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

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

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

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

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

null is the singleton null JSON value.

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

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

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

object_(dict) makes a JSON object of the dict.

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

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

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

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

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

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

See parse on MDN.

Examples

RESCRIPT
/* parse a simple JSON string */

let json = try Js.Json.parseExn(` "hello" `) catch {
| _ => failwith("Error parsing JSON string")
}

switch Js.Json.classify(json) {
| Js.Json.JSONString(value) => Js.log(value)
| _ => failwith("Expected a string")
}

RESCRIPT
/* parse a complex JSON string */

let getIds = s => {
  let json = try Js.Json.parseExn(s) catch {
  | _ => failwith("Error parsing JSON string")
  }

  switch Js.Json.classify(json) {
  | Js.Json.JSONObject(value) =>
    /* In this branch, compiler infer value : Js.Json.t dict */
    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(json) formats the JSON data structure as a string. Returns the string representation of a given JSON data structure.

See stringify on MDN.

Examples

RESCRIPT
/* 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(["ReScript", "ocaml", "js"]))

Js.log(Js.Json.stringify(Js.Json.object_(dict)))

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

See stringify on MDN.

Examples

RESCRIPT
/* 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(["ReScript", "ocaml", "js"]))

Js.log(Js.Json.stringifyWithSpace(Js.Json.object_(dict), 2))

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

Examples

RESCRIPT
/* prints `["hello", "world"]` */
Js.log(Js.Json.stringifyAny(["hello", "world"]))

Best-effort serialization, it tries to seralize as many objects as possible and deserialize it back

It is unsafe in two aspects

• It may throw during parsing

• when you cast it to a specific type, it may have a type mismatch

It will throw in such situations:

• The object can not be serlialized to a JSON

• There are cycles

• Some JS engines can not stringify deeply nested json objects