Merge branch 'bookcreator-master'

index.js

@@ -39,12 +39,18 @@ const wrapFunction = fn =>
         const result = fn.call(this, chunk, encoding);
         if (result && typeof result.then == 'function') {
           // thenable
-          result.then(result => (Chain.sanitize(result, this), callback(null)), error => callback(error));
+          result.then(
+            result => (Chain.sanitize(result, this), callback(null)),
+            error => callback(error)
+          );
           return;
         }
         if (result && typeof result.next == 'function') {
           // generator
-          runAsyncGenerator(result, this).then(() => callback(null), error => callback(error));
+          runAsyncGenerator(result, this).then(
+            () => callback(null),
+            error => callback(error)
+          );
           return;
         }
         Chain.sanitize(result, this);
@@ -82,6 +88,23 @@ const wrapArray = fns =>
     }
   });
 
+// is*NodeStream functions taken from https://github.com/nodejs/node/blob/master/lib/internal/streams/utils.js
+const isReadableNodeStream = obj =>
+  obj &&
+  typeof obj.pipe === 'function' &&
+  typeof obj.on === 'function' &&
+  (!obj._writableState || (typeof obj._readableState === 'object' ? obj._readableState.readable : null) !== false) && // Duplex
+  (!obj._writableState || obj._readableState); // Writable has .pipe.
+
+const isWritableNodeStream = obj =>
+  obj &&
+  typeof obj.write === 'function' &&
+  typeof obj.on === 'function' &&
+  (!obj._readableState || (typeof obj._writableState === 'object' ? obj._writableState.writable : null) !== false); // Duplex
+
+const isDuplexNodeStream = obj =>
+  obj && typeof obj.pipe === 'function' && obj._readableState && typeof obj.on === 'function' && typeof obj.write === 'function';
+
 class Chain extends Duplex {
   constructor(fns, options) {
     super(options || {writableObjectMode: true, readableObjectMode: true});
@@ -94,12 +117,7 @@ class Chain extends Duplex {
       .filter(fn => fn)
       .map((fn, index, fns) => {
         if (typeof fn === 'function' || fn instanceof Array) return Chain.convertToTransform(fn);
-        if (
-          fn instanceof Duplex ||
-          fn instanceof Transform ||
-          (!index && fn instanceof Readable) ||
-          (index === fns.length - 1 && fn instanceof Writable)
-        ) {
+        if (isDuplexNodeStream(fn) || (!index && isReadableNodeStream(fn)) || (index === fns.length - 1 && isWritableNodeStream(fn))) {
           return fn;
         }
         throw Error('Arguments should be functions, arrays or streams.');
@@ -108,13 +126,13 @@ class Chain extends Duplex {
     this.input = this.streams[0];
     this.output = this.streams.reduce((output, stream) => (output && output.pipe(stream)) || stream);
 
-    if (!(this.input instanceof Writable)) {
+    if (!isWritableNodeStream(this.input)) {
       this._write = (_1, _2, callback) => callback(null);
       this._final = callback => callback(null); // unavailable in Node 6
       this.input.on('end', () => this.end());
     }
 
-    if (this.output instanceof Readable) {
+    if (isReadableNodeStream(this.output)) {
       this.output.on('data', chunk => !this.push(chunk) && this.output.pause());
       this.output.on('end', () => this.push(null));
     } else {