Basic gzip an gunzip on load and save.

utils/polyfills.js

@@ -14,3 +14,20 @@ if (Array.prototype.flat === undefined) {
     return this.reduce((acc, val) => (Array.isArray(val) ? acc.concat(val.flat()) : acc.concat(val)), []);
   };
 }
+
+// polyfill readable stream iterator: https://bugs.chromium.org/p/chromium/issues/detail?id=929585#c10
+if(ReadableStream.prototype[Symbol.asyncIterator] === undefined){
+  ReadableStream.prototype[Symbol.asyncIterator] = async function* () {
+    const reader = this.getReader()
+    try {
+      while (true) {
+        const {done, value} = await reader.read()
+        if (done) return
+        yield value
+      }
+    }
+    finally {
+      reader.releaseLock()
+    }
+  }
+}