Fix the WASM example for the coordinate mapping

Author: 38

examples/wasm-demo/www/index.js

@@ -43,10 +43,18 @@ function setupCanvas() {
 /** Update displayed coordinates. */
 function onMouseMove(event) {
     if (chart) {
-        const point = chart.coord(event.offsetX, event.offsetY);
-        coord.innerText = (point)
-            ? `(${point.x.toFixed(3)}, ${point.y.toFixed(3)})`
-            : "Mouse pointer is out of range";
+		var text = "Mouse pointer is out of range";
+
+		if(event.target == canvas) {
+			let actualRect = canvas.getBoundingClientRect();
+			let logicX = event.offsetX * canvas.width / actualRect.width;
+			let logicY = event.offsetY * canvas.height / actualRect.height;
+			const point = chart.coord(logicX, logicY);
+			text = (point) 
+				? `(${point.x.toFixed(3)}, ${point.y.toFixed(3)})`
+				: text;
+		}
+        coord.innerText = text;
     }
 }