3 files changed, 45 insertions, 1 deletions
diff --git a/ext/wasm/api/extern-post-js.js b/ext/wasm/api/extern-post-js.js
index acb54c3c9..25d2d1b32 100644
--- a/ext/wasm/api/extern-post-js.js
+++ b/ext/wasm/api/extern-post-js.js
@@ -1,4 +1,4 @@
-/* emscripten-js-addenda.js must be appended to the resulting sqlite3.js
+/* extern-post-js.js must be appended to the resulting sqlite3.js
    file. */
 (function(){
   /**
diff --git a/ext/wasm/api/extern-pre-js.js b/ext/wasm/api/extern-pre-js.js
new file mode 100644
index 000000000..26d066d2e
--- /dev/null
+++ b/ext/wasm/api/extern-pre-js.js
@@ -0,0 +1,4 @@
+/* extern-pre-js.js must be prepended to the resulting sqlite3.js
+   file. This file is currently only used for holding snippets during
+   test and development.
+*/
diff --git a/ext/wasm/api/pre-js.js b/ext/wasm/api/pre-js.js
new file mode 100644
index 000000000..f373fecec
--- /dev/null
+++ b/ext/wasm/api/pre-js.js
@@ -0,0 +1,40 @@
+Module['locateFile'] = function(path, prefix) {
+  return prefix + path;
+};
+
+/**
+   Bug warning: this xInstantiateWasm bit must remain disabled
+   until this bug is resolved or wasmfs won't work:
+
+   https://github.com/emscripten-core/emscripten/issues/17951
+*/
+const xInstantiateWasm = 1
+      ? 'emscripten-bug-17951'
+      : 'instantiateWasm';
+Module[xInstantiateWasm] = function callee(imports,onSuccess){
+  imports.foo = function(){};
+  console.warn("instantiateWasm() uri =",callee.uri, self.location.href);
+  const wfetch = ()=>fetch(callee.uri, {credentials: 'same-origin'});
+  const loadWasm = WebAssembly.instantiateStreaming
+        ? function loadWasmStreaming(){
+          return WebAssembly.instantiateStreaming(wfetch(), imports)
+            .then((arg)=>onSuccess(arg.instance, arg.module));
+        }
+        : function loadWasmOldSchool(){ // Safari < v15
+          return wfetch()
+            .then(response => response.arrayBuffer())
+            .then(bytes => WebAssembly.instantiate(bytes, imports))
+            .then((arg)=>onSuccess(arg.instance, arg.module));
+        };
+  loadWasm();
+  return {};
+};
+/*
+  It is literally impossible to get the name of a Worker's own script,
+  so impossible to derive X.wasm from script name X.js. Thus we need,
+  at build-time, to redifine Module['instantiateWasm'].uri by
+  appending it to a build-specific copy of this file with the name of
+  the wasm file. This is apparently why Emscripten hard-codes the name of
+  the wasm file into their glue scripts.
+*/
+Module[xInstantiateWasm].uri = 'sqlite3.wasm';