diff --git a/src/cavnas.js b/src/cavnas.js
index ccc4c2b..761cb3c 100644
--- a/src/cavnas.js
+++ b/src/cavnas.js
@@ -1,13 +1,13 @@
-let globaCanvas;
+let globalCanvas;
 
 export function getCanvas(tileSize = 256) {
-    if (!globaCanvas && OffscreenCanvas) {
-        globaCanvas = new OffscreenCanvas(1, 1);
+    if (!globalCanvas && OffscreenCanvas) {
+        globalCanvas = new OffscreenCanvas(1, 1);
     }
-    if (globaCanvas) {
-        globaCanvas.width = globaCanvas.height = tileSize;
+    if (globalCanvas) {
+        globalCanvas.width = globalCanvas.height = tileSize;
     }
-    return globaCanvas;
+    return globalCanvas;
 }
 
 function clearCanvas(ctx) {
diff --git a/src/tileclip.js b/src/tileclip.js
index 08629b5..14abe3d 100644
--- a/src/tileclip.js
+++ b/src/tileclip.js
@@ -14,7 +14,7 @@ export function isPolygon(feature) {
     return type === 'Polygon' || type === 'MultiPolygon';
 }
 
-export function is3857(projection) {
+export function isEPSG3857(projection) {
     return projection === 'EPSG:3857';
 }
 
@@ -48,7 +48,7 @@ function lnglat2Mercator(coordinates) {
 }
 
 function transformCoordinates(projection, coordinates) {
-    if (!is3857(projection)) {
+    if (!isEPSG3857(projection)) {
         return coordinates;
     } else {
         const transformRing = (coord) => {
@@ -91,7 +91,7 @@ function transformPixels(projection, tileBBOX, tileSize, coordinates) {
         }
         return result;
     };
-    if (is3857(projection)) {
+    if (isEPSG3857(projection)) {
         const [mminx, mminy] = lnglat2Mercator([minx, miny]);
         const [mmaxx, mmaxy] = lnglat2Mercator([maxx, maxy]);
         const mTileBBOX = [mminx, mminy, mmaxx, mmaxy];
diff --git a/src/worker.js b/src/worker.js
index 25e6c6d..d2f048d 100644
--- a/src/worker.js
+++ b/src/worker.js
@@ -23,6 +23,7 @@ export const onmessage = function (message, postResponse) {
             return;
         }
         postResponse(null, image, [image]);
+        return;
     }
     if (type === 'injectMask') {
         const geojson = injectMask(data.maskId, data.geojsonFeature);
@@ -31,9 +32,12 @@ export const onmessage = function (message, postResponse) {
             return;
         }
         postResponse();
+        return;
     }
     if (type === 'removeMask') {
         removeMask(data.maskId);
         postResponse();
+        return;
     }
+    console.error('not support message type:', type);
 };