Module Js.Json

module Json: Js_json

Types

type t 
The JSON data structure
type '_ kind = 
| String : Js_string.t kind
| Number : float kind
| Object : t Js_dict.t kind
| Array : t array kind
| Boolean : bool kind
| Null : Js_types.null_val kind
Underlying type of a JSON value
type tagged_t = 
| JSONFalse
| JSONTrue
| JSONNull
| JSONString of string
| JSONNumber of float
| JSONObject of t Js_dict.t
| JSONArray of t array

Accessor

val classify : t -> tagged_t
val test : 'a -> 'b kind -> bool
test v kind returns true if v is of kind
val decodeString : t -> Js_string.t option
decodeString json returns Some s if json is a string, None otherwise
val decodeNumber : t -> float option
decodeNumber json returns Some n if json is a number, None otherwise
val decodeObject : t -> t Js_dict.t option
decodeObject json returns Some o if json is an object, None otherwise
val decodeArray : t -> t array option
decodeArray json returns Some a if json is an array, None otherwise
val decodeBoolean : t -> bool option
decodeBoolean json returns Some b if json is a boolean, None otherwise
val decodeNull : t -> 'a Js_null.t option
decodeNull json returns Some null if json is a null, None otherwise

Construtors

Those functions allows the construction of an arbitrary complex JSON values.

val null : t
null is the singleton null JSON value
val string : string -> t
string s makes a JSON string of the string s
val number : float -> t
number n makes a JSON number of the float n
val boolean : bool -> t
boolean b makes a JSON boolean of the bool b
val object_ : t Js_dict.t -> t
object_ dict makes a JSON object of the Js.Dict.t dict
val array : t array -> t
array_ a makes a JSON array of the Js.Json.t array a

The functions below are specialized for specific array type which happened to be already JSON object in the BuckleScript runtime. Therefore they are more efficient (constant time rather than linear conversion).

val stringArray : string array -> t
stringArray a makes a JSON array of the string array a
val numberArray : float array -> t
numberArray a makes a JSON array of the float array a
val booleanArray : bool array -> t
booleanArray makes a JSON array of the bool array a
val objectArray : t Js_dict.t array -> t
objectArray a makes a JSON array of the JsDict.t array a

String conversion

val parseExn : string -> t
parseExn s parses the string s into a JSON data structure Returns a JSON data structure
  • Raises SyntaxError if given string is not a valid JSON. Note SyntaxError is a JavaScript exception.
  • See also MDN
  •  
    (* parse a simple JSON string *)
    
    let json =
      try
        Js.Json.parseExn {| "foo" |}
      with
      | _ -> failwith "Error parsing JSON string"
    in
    match Js.Json.classify json with
    | Js.Json.JSONString value -> Js.log value
    | _ -> failwith "Expected a string"
    
     
    (* parse a complex JSON string *)
    
    let getIds s =
      let json =
        try
          Js.Json.parseExn s
        with
        | _ -> failwith "Error parsing JSON string"
      in
      match Js.Json.classify json with
      | Js.Json.JSONObject value ->
        (* In this branch, compiler infer value : Js.Json.t Js.Dict.t *)
        begin match Js.Dict.get value "ids" with
        | Some ids ->
          begin match Js.Json.classify ids with
          | Js.Json.JSONArray ids ->
            (* In this branch compiler infer ids : Js.Json.t array *)
            ids
          | _ -> failwith "Expected an array"
          end
        | None -> failwith "Expected an `ids` property"
        end
      | _ -> failwith "Expected an object"
    
    (* prints `1, 2, 3` *)
    let _ =
      Js.log @@ getIds {| { "ids" : [1, 2, 3 ] } |}
    
    val stringify : t -> string
    stringify json formats the JSON data structure as a string Returns the string representation of a given JSON data structure
  • See also MDN
  •  
    (* Creates and stringifies a simple JS object *)
    
    let dict = Js.Dict.empty () in 
    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) 
    
    val stringifyWithSpace : t -> int -> string
    stringify json formats the JSON data structure as a string Returns the string representation of a given JSON data structure
  • See also MDN
  •  
    (* Creates and stringifies a simple JS object with spacing *)
    
    let dict = Js.Dict.empty () in 
    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
    
    val stringifyAny : 'a -> string option
    stringifyAny value formats any value into a JSON string
  • See also MDN
  •  
    (* prints `["foo", "bar"]` *)
    Js.log @@ Js.Json.stringifyAny [| "foo"; "bar" |]