diff --git a/src/playground/playground.js b/src/playground/playground.js
index 0b288f1..4cc8c42 100644
--- a/src/playground/playground.js
+++ b/src/playground/playground.js
@@ -37,7 +37,7 @@ image.src = 'https://cdn.assets.scratch.mit.edu/internalapi/asset/7e24c99c1b853e
 
 // SVG (cat 1-a)
 const xhr = new XMLHttpRequest();
-xhr.addEventListener('load', function () {
+xhr.addEventListener('load', () => {
     const skinId = renderer.createSVGSkin(xhr.responseText);
     if (wantedSkin === WantedSkinType.vector) {
         renderer.updateDrawableProperties(drawableID2, {
@@ -56,10 +56,10 @@ if (wantedSkin === WantedSkinType.pen) {
     });
 
     canvas.addEventListener('click', event => {
-        let rect = canvas.getBoundingClientRect();
+        const rect = canvas.getBoundingClientRect();
 
-        let x = event.clientX - rect.left;
-        let y = event.clientY - rect.top;
+        const x = event.clientX - rect.left;
+        const y = event.clientY - rect.top;
 
         renderer.penLine(penSkinID, {
             color4f: [Math.random(), Math.random(), Math.random(), 1],
@@ -184,7 +184,7 @@ canvas.addEventListener('mousemove', event => {
 canvas.addEventListener('click', event => {
     const mousePos = getMousePosition(event, canvas);
     const pickID = renderer.pick(mousePos.x, mousePos.y);
-    console.log('You clicked on ' + (pickID < 0 ? 'nothing' : 'ID# ' + pickID));
+    console.log(`You clicked on ${(pickID < 0 ? 'nothing' : `ID#${pickID}`)}`);
     if (pickID >= 0) {
         console.dir(renderer.extractDrawable(pickID, mousePos.x, mousePos.y));
     }
diff --git a/src/playground/queryPlayground.js b/src/playground/queryPlayground.js
index 7befdf7..0d124bd 100644
--- a/src/playground/queryPlayground.js
+++ b/src/playground/queryPlayground.js
@@ -92,9 +92,9 @@ renderCanvas.addEventListener('click', event => {
     }
 });
 
-const rgb2fillStyle = (rgb) => {
-    return `rgb(${rgb[0]},${rgb[1]},${rgb[2]})`;
-};
+const rgb2fillStyle = rgb => (
+    `rgb(${rgb[0]},${rgb[1]},${rgb[2]})`
+);
 
 const makeCursorImage = () => {
     const canvas = document.createElement('canvas');