Ppx syntax extension for Js_of_ocaml
To migrate from the camlp4 extension, it is advised to use camlp4-to-ppx which provides built-in support for Js_of_ocaml syntax.
A ppx rewriter (syntax extension) is available for manipulating object properties, invoking methods and creating objects.
The syntax and typing rules are as follows:
- Getting a property
obj : <m : u Js.prop> Js.t -------------------------- obj##.m : u
- Setting a property
obj : <m : u Js.prop> Js.t e : u -------------------------- obj##.m := e : unit
- Invoking a method
obj : <m : t_1 -> ... -> t_n -> u Js.meth; ..> Js.t e_i : t_i (1 <= i <= n) ---------------------------------------------------- obj##m e_1 ... e_n : u
For easier chaining, the following alternative syntax is also possible: [ obj(m e_1 ... e_n) ].
Beware, partial application is not allowed.
- Using an object constructor
constr : (t_1 -> ... -> t_n -> u Js.t) Js.constr e_i : t_i (1 <= i <= n) ------------------------------------------------ new%js constr e1 ... en : u Js.t
[ constr ] here must be an identifier. For constructors that are not identifiers, bind them first:
let a = Js.Unsafe.global##.A in
new%js a
- Creating a literal object
object%js (self) (* Equivalent of this *)
val x1 = 3 (* read-only prop *)
val x2 = 3 [@@readonly] (* read-only prop *)
val mutable y1 = 4 (* read/write prop *)
val y2 = 4 [@@readwrite] (* read/write prop *)
val z = 5 [@@writeonly] (* write-only prop *)
val t1 = Js.undefined [@@jsoo.optdef] (* optdef prop *)
method foo i = self##.y1 := self##.x1 + i
end
Properties are defined with the [val] keyword. [mutable] makes the property writable. Properties can be annotated with attributes to change the default semantic. Attributes can be one of [readwrite], [readonly], [writeonly], [optdef].
[self] can be any identifier and will be bind to [this] in javascript.
In this case, the object has the following type:
< foo : int -> unit Js.meth;
t1 : 'a Js.optdef_prop;
x1 : int Js.readonly_prop;
x2 : int Js.readonly_prop;
y1 : int Js.prop;
y2 : int Js.prop;
z : int Js.writeonly_prop >
Js.t