Optipng (#156)

* omg it’s compiling

* example actually works

* Expose compression level options

* Disable crypto and path module emulation in webpack

* Update README

* Remove small image

* Use -O3 on optipng

* Free memory after copy

* Handle unexpected file reader return types

* Rename level label to effort

src/lib/util.ts

@@ -106,10 +106,13 @@ export function canDecodeImage(data: string): Promise<boolean> {
 }
 
 export function blobToArrayBuffer(blob: Blob): Promise<ArrayBuffer> {
-  return new Promise((resolve) => {
+  return new Promise((resolve, reject) => {
     const fileReader = new FileReader();
     fileReader.addEventListener('load', () => {
-      resolve(fileReader.result);
+      if (fileReader.result instanceof ArrayBuffer) {
+        return resolve(fileReader.result);
+      }
+      reject(Error('Unexpected return type'));
     });
     fileReader.readAsArrayBuffer(blob);
   });