add basic infrastructure of javascript example

example/provider/javascript/js/webfuse/messagewriter.js

@@ -0,0 +1,76 @@
+class MessageWriter {
+
+    constructor(message_id, message_type) {
+        this.data = [ ]
+        this.write_u32(message_id)
+        this.write_u8(message_type)
+        this.encoder = new TextEncoder("utf-8");
+    }
+
+    write_u8(value) {
+        this.data.push(value)
+    }
+
+    write_u32(value) {
+        const buffer = new ArrayBuffer(4);
+        const view = new DataView(buffer);
+        view.setUint32(0, value);
+
+        const data = new Uint8Array(buffer);
+        this.data.push(...data);
+    }
+
+    write_i32(value) {
+        const buffer = new ArrayBuffer(4);
+        const view = new DataView(buffer);
+        view.setInt32(0, value);
+
+        const data = new Uint8Array(buffer);
+        this.data.push(...data);
+    }
+
+    write_u64(value) {
+        const buffer = new ArrayBuffer(8);
+        const view = new DataView(buffer);
+        view.setBigUint64(0, BigInt(value));
+
+        const data = new Uint8Array(buffer);
+        this.data.push(...data);
+    }
+
+    // value in milliseconds
+    write_time(value) {
+        const seconds = Math.floor(value / 1000);
+        const millis = value % 1000;
+        const nanos = millis * 1000 * 1000;
+
+        this.write_u64(seconds);
+        this.write_u32(nanos);
+    }
+
+    write_str(value) {
+        const data = this.encoder.encode(value);
+        this.write_u32(data.length);
+        this.data.push(...data);
+    }
+
+    write_strings(list) {
+        this.write_u32(list.length);
+        for(const item of list) {
+            this.write_str(item);
+        }
+    }
+
+    write_bytes(value) {
+        this.write_u32(value.length);
+        this.data.push(...value);
+    }
+
+    get_data() {
+        // console.log(this.data)
+        return new Uint8Array(this.data);
+    }
+
+}
+
+export { MessageWriter }