Initial bits for a JS API variant in which the client operates in the main thread and sqlite3 in a Worker. This is far from complete.

FossilOrigin-Name: f6d6f969791f0d2367ae5418623b4794f6df657d9d7d9002fb5aec4206dcfd4c

ext/fiddle/testing2.js

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+/*
+  2022-05-22
+
+  The author disclaims copyright to this source code.  In place of a
+  legal notice, here is a blessing:
+
+  *   May you do good and not evil.
+  *   May you find forgiveness for yourself and forgive others.
+  *   May you share freely, never taking more than you give.
+
+  ***********************************************************************
+
+  A basic test script for sqlite3-worker.js.
+*/
+(function(){
+    /** Posts a worker message as {type:type, data:data}. */
+    const SW = new Worker("sqlite3-worker.js");
+    const wMsg = (type,data)=>SW.postMessage({type, data});
+    const log = console.log.bind(console);
+    const warn = console.warn.bind(console);
+    SW.onmessage = function(ev){
+        if(!ev.data || 'object'!==typeof ev.data){
+            warn("Unknown sqlite3-worker message type:",ev);
+            return;
+        }
+        ev = ev.data/*expecting a nested object*/;
+        switch(ev.type){
+            case 'sqlite3-api':
+                switch(ev.data){
+                    case 'loaded':
+                        log("Message:",ev); return;
+                    case 'ready':
+                        log("Message:",ev);
+                        self.sqlite3TestModule.setStatus(null);
+                        return;
+                    default: break;
+                }
+                break;
+        }
+        warn("Unknown sqlite3-api message type:",ev);
+    };
+    log("Init complete, but async bits may still be running.");
+})();