runtime(js): better caml_xmlhttprequest_create error handling and remove Map polyfill

[smorimoto]

This PR enhances error handling in the caml_xmlhttprequest_create implementation and removes the unnecessary Map polyfill to simplify the MlObjectTable implementation. It provides more detailed error messages when caml_xmlhttprequest_create fails and updates documentation to reflect the use of these APIs.

[Copilot]

PR Overview

This PR simplifies runtime checks in JavaScript runtime code by removing redundant existence validations and the polyfill for legacy environments.

• Simplifies XMLHttpRequest creation in jslib_js_of_ocaml.js by removing an unnecessary type check and catch parameter
• Eliminates the legacy polyfill for MlObjectTable in marshal.js in favor of using globalThis.Map exclusively

Reviewed Changes

File	Description
runtime/js/jslib_js_of_ocaml.js	Simplifies XMLHttpRequest creation by removing extra checks and a catch parameter
runtime/js/marshal.js	Removes the legacy polyfill for MlObjectTable, relying solely on globalThis.Map

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

Comments suppressed due to low confidence (1)

runtime/js/marshal.js:633

• Removing the polyfill for environments where globalThis.Map is undefined may cause failures in older runtimes. Ensure that your target environments fully support globalThis.Map.

function MlObjectTable() {

[Copilot]

Using a catch block without an error binding may obscure useful error details, which could hinder debugging. Consider capturing the error (e.g., using 'catch (e)') to log or examine further.

Suggested change

	} catch {
	} catch (e) {
	console.error("Error creating XMLHttpRequest:", e);

[smorimoto]

This can be added if you prefer @hhugo

[hhugo]

I think I prefer the version before this PR. XMLHttpRequest might not be defined (e.g. node) and the code reflected that.

[smorimoto]

So instead of an error message that it could not be created, should it be an error message saying it is not available?

[smorimoto]

Or

function caml_xmlhttprequest_create(unit) {
  if (typeof globalThis.XMLHttpRequest === "undefined") {
    caml_failwith("XMLHttpRequest is not available");
  }

  try {
    return new globalThis.XMLHttpRequest();
  } catch {
    caml_failwith("Failed to create XMLHttpRequest");
  }
}

[hhugo]

Maybe but this non longer fit in the PR title and description as it's no longer a simplification and no longer remove checks

[smorimoto]

@hhugo Well, I just updated the title and description of the PR, but if it's better to drop the commit itself, I will drop it.

[Copilot]

PR Overview

This pull request removes outdated runtime polyfills, requiring native support for JavaScript's Map and XMLHttpRequest to simplify the code and reduce bundle size.

• Removed the Map polyfill from the MlObjectTable implementation and now relies on native Map support.
• Simplified the XMLHttpRequest creation function by directly using the global implementation and throwing clear error messages.
• Updated documentation in ECMASCRIPT.md and release notes in CHANGES.md to reflect these changes.

Reviewed Changes

File	Description
ECMASCRIPT.md	Added new sections for Map and XMLHttpRequest compatibility
runtime/js/jslib_js_of_ocaml.js	Refined XMLHttpRequest creation logic with improved error handling
CHANGES.md	Updated release notes with polyfill removal and XMLHttpRequest changes
runtime/js/marshal.js	Removed the Map polyfill from MlObjectTable implementation

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (1)

runtime/js/jslib_js_of_ocaml.js:81

• [nitpick] Consider capturing the error object in the catch block (e.g., 'catch (e)') and including its message in the call to caml_failwith to provide additional debugging context.

  } catch {