Node.js and XMLHttpRequest

[MaillPierre]

Trying to port a browser-based library to Node.js, i get errors during AJAX calls through XmlHttpRequest:

File "lib/xmlHttpRequest.ml", line 86, characters 2-8: Assertion failed

Is there an established method to be able to use xmlHttpRequest from ocaml code on a Node.js server ?

[MaillPierre]

I bypassed the problem with a custom xhr creation function:

let create_xhr () : xmlHttpRequest Js.t =
  let xmlHttpRequest =
    if Js.Optdef.test (Js.def Js.Unsafe.global##._XMLHttpRequest) then
      Js.Unsafe.global##._XMLHttpRequest 
      else if Js.Optdef.test (Js.def (Js.Unsafe.pure_js_expr "require('xmlhttprequest').XMLHttpRequest")) then 
      (Js.Unsafe.pure_js_expr "require('xmlhttprequest').XMLHttpRequest") else 
      assert false in
  let activeXObject = Js.Unsafe.global##.activeXObject in
  try new%js xmlHttpRequest with _ ->
  try new%js activeXObject (Js.string "Msxml2.XMLHTTP") with _ ->
  try new%js activeXObject (Js.string "Msxml3.XMLHTTP") with _ ->
  try new%js activeXObject (Js.string "Microsoft.XMLHTTP") with _ ->
  assert false

[Lupus]

I've ran into the same issue. @MaillPierre do you use your create_xhr directly? I'm trying to port some Cohttp based code and it dies because of missing XMLHttpRequest. All my attemepts to provide some runtime file to js_of_ocaml which sets global XMLHttpRequest to be require('xmlhttprequest').XMLHttpRequest failed so far. Forking Cohttp xhr Client module and modifying it sounds like a lot of maintenance burden. Isn't there a better solution?

[Lupus]

Another ugly workaround: create a file xmlhttprequest_preload.js with the following content:

global.XMLHttpRequest = require("xmlhttprequest").XMLHttpRequest;

Run your service as follows:

$ nodejs -r ./xmlhttprequest_preload.js your_service.bc.js

[Lupus]

@hhugo what if create () will be defined as external function with implementation in js_of_ocaml runtime as a primitive? This way users can override this primitive in their own runtime files and provide alternate implementation for Node.js.

[hhugo]

@Lupus, that sounds very good to me !