1 files changed, 42 insertions, 2 deletions
diff --git a/ext/wasm/api/pre-js.js b/ext/wasm/api/pre-js.js
index b6630416d..c07d0373c 100644
--- a/ext/wasm/api/pre-js.js
+++ b/ext/wasm/api/pre-js.js
@@ -4,9 +4,49 @@
    This file is intended to be prepended to the sqlite3.js build using
    Emscripten's --pre-js=THIS_FILE flag (or equivalent).
 */
+
+// See notes in extern-post-js.js
+const sqlite3InitModuleState = self.sqlite3InitModuleState || Object.create(null);
+delete self.sqlite3InitModuleState;
+
+/**
+   This custom locateFile() tries to figure out where to load `path`
+   from. The intent is to provide a way for foo/bar/X.js loaded from a
+   Worker constructor or importScripts() to be able to resolve
+   foo/bar/X.wasm (in the latter case, with some help):
+
+   1) If URL param named the same as `path` is set, it is returned.
+
+   2) If sqlite3InitModuleState.sqlite3Dir is set, then (thatName + path)
+      is returned (note that it's assumed to end with '/').
+
+   3) If this code is running in the main UI thread AND it was loaded
+      from a SCRIPT tag, the directory part of that URL is used
+      as the prefix. (This form of resolution unfortunately does not
+      function for scripts loaded via importScripts().)
+
+   4) If none of the above apply, (prefix+path) is returned.
+*/
 Module['locateFile'] = function(path, prefix) {
-  return prefix + path;
-};
+  let theFile;
+  const up = this.urlParams;
+  if(0){
+    console.warn("locateFile(",arguments[0], ',', arguments[1],")",
+                 'self.location =',self.location,
+                 'sqlite3InitModuleState.scriptDir =',this.scriptDir,
+                 'up.entries() =',Array.from(up.entries()));
+  }
+  if(up.has(path)){
+    theFile = up.get(path);
+  }else if(this.sqlite3Dir){
+    theFile = this.sqlite3Dir + path;
+  }else if(this.scriptDir){
+    theFile = this.scriptDir + path;
+  }else{
+    theFile = prefix + path;
+  }
+  return theFile;
+}.bind(sqlite3InitModuleState);
 
 /**
    Bug warning: this xInstantiateWasm bit must remain disabled