Implements getQuickJSImmediate (bellard#16)

* Implements getQuickJSImmediate

* Update quickjs.ts

* Prettier

Author: arcanis

README.md

@@ -41,6 +41,9 @@ The root entrypoint of this library is the `getQuickJS` function, which returns
 a promise that resolves to a [QuickJS singleton](doc/classes/quickjs.md) when
 the Emscripten WASM module is ready.
 
+Once `getQuickJS` has been awaited at least once, you also can use the `getQuickJSImmediate`
+function to directly access the singleton engine in your synchronous code.
+
 ### Safely evaluate Javascript code
 
 See [QuickJS.evalCode](https://github.com/justjake/quickjs-emscripten/blob/master/doc/classes/quickjs.md#evalcode)

ts/quickjs.ts

@@ -984,3 +984,14 @@ export async function getQuickJS(): Promise<QuickJS> {
   }
   return singleton
 }
+
+/**
+ * This is the top-level entrypoint for the quickjs-emscripten library.
+ * Get the root QuickJS API.
+ */
+export function getQuickJSImmediate(): QuickJS {
+  if (!singleton) {
+    throw new Error('QuickJS not initialized. Either wait for `ready` or use getQuickJS()')
+  }
+  return singleton
+}