fix(fetch): fixed ReferenceError issue when TextEncoderis not avail…

…able in the environment;

lib/adapters/fetch.js

@@ -20,6 +20,12 @@ const fetchProgressDecorator = (total, fn) => {
 const isFetchSupported = typeof fetch !== 'undefined';
 const isReadableStreamSupported = isFetchSupported && typeof ReadableStream !== 'undefined';
 
+// used only inside the fetch adapter
+const encodeText = isFetchSupported && (typeof TextEncoder !== 'undefined' ?
+    ((encoder) => (str) => encoder.encode(str))(new TextEncoder()) :
+    async (str) => new Uint8Array(await new Response(str).arrayBuffer())
+);
+
 const supportsRequestStream = isReadableStreamSupported && (() => {
   let duplexAccessed = false;
 
@@ -80,7 +86,7 @@ const getBodyLength = async (body) => {
   }
 
   if(utils.isString(body)) {
-    return (await new TextEncoder().encode(body)).byteLength;
+    return (await encodeText(body)).byteLength;
   }
 }
 
@@ -144,7 +150,7 @@ export default isFetchSupported && (async (config) => {
         data = trackStream(_request.body, DEFAULT_CHUNK_SIZE, fetchProgressDecorator(
           requestContentLength,
           progressEventReducer(onUploadProgress)
-        ));
+        ), null, encodeText);
       }
     }
 
@@ -179,7 +185,7 @@ export default isFetchSupported && (async (config) => {
         trackStream(response.body, DEFAULT_CHUNK_SIZE, onDownloadProgress && fetchProgressDecorator(
           responseContentLength,
           progressEventReducer(onDownloadProgress, true)
-        ), isStreamResponse && onFinish),
+        ), isStreamResponse && onFinish, encodeText),
         options
       );
     }

lib/helpers/trackStream.js

@@ -1,4 +1,5 @@
 
+
 export const streamChunk = function* (chunk, chunkSize) {
   let len = chunk.byteLength;
 
@@ -17,16 +18,14 @@ export const streamChunk = function* (chunk, chunkSize) {
   }
 }
 
-const encoder = new TextEncoder();
-
-export const readBytes = async function* (iterable, chunkSize) {
+export const readBytes = async function* (iterable, chunkSize, encode) {
   for await (const chunk of iterable) {
-    yield* streamChunk(ArrayBuffer.isView(chunk) ? chunk : (await encoder.encode(String(chunk))), chunkSize);
+    yield* streamChunk(ArrayBuffer.isView(chunk) ? chunk : (await encode(String(chunk))), chunkSize);
   }
 }
 
-export const trackStream = (stream, chunkSize, onProgress, onFinish) => {
-  const iterator = readBytes(stream, chunkSize);
+export const trackStream = (stream, chunkSize, onProgress, onFinish, encode) => {
+  const iterator = readBytes(stream, chunkSize, encode);
 
   let bytes = 0;