add renderSyncToString API

CHANGELOG.md

@@ -1,5 +1,7 @@
 # master
 
+- Add `renderSyncToString` API.
+
 # 0.1.0-beta.2
 
 - Bind basic version of `hxTarget`.

src/H.res

@@ -8,6 +8,11 @@ external array: array<Jsx.element> => Jsx.element = "%identity"
 @module("./vendor/hyperons.js")
 external renderToString: Jsx.element => promise<string> = "render"
 
+/** Renders a subtree to content. Throws if the subtree is asynchronous. */
+@module("./vendor/hyperons.js")
+@raises(Js.Exn.t)
+external renderSyncToString: Jsx.element => string = "renderSync"
+
 @module("./vendor/hyperons.js")
 external renderToStream: (Jsx.element, ~onChunk: string => unit=?) => promise<unit> = "render"
 

src/vendor/hyperons.js

@@ -291,6 +291,15 @@ async function render(element, onChunk) {
     return res;
   }
 }
+function renderSync(element) {
+  const controller = makeController();
+  renderToString(element, {}, controller);
+  if (controller.hasAsync) {
+    throw new Error("Tried to render async tree sync.");
+  } else {
+    return controller.content.join("");
+  }
+}
 function useContext(instance) {
   return instance.getChildContext(dispatcher.context);
 }
@@ -299,6 +308,7 @@ export {
   createContext,
   createElement as h,
   render,
+  renderSync,
   useContext,
   escapeString,
 };