Initial commit.

.editorconfig

@@ -0,0 +1,9 @@
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+indent_style = space
+indent_size = 2

.gitignore

@@ -0,0 +1,4 @@
+node_modules/*
+report/*
+coverage/*
+.AppleDouble

.prettierrc

@@ -0,0 +1,5 @@
+{
+  "printWidth": 120,
+  "singleQuote": true,
+  "bracketSpacing": false
+}

.travis.yml

@@ -0,0 +1,8 @@
+sudo: false
+
+language: node_js
+
+node_js:
+  - "6"
+  - "8"
+  - "10"

main.js

@@ -0,0 +1,75 @@
+'use strict';
+
+const EventEmitter = require('events');
+const {Transform} = require('stream');
+
+const GeneratorFunction = Object.getPrototypeOf(function*() {}).constructor;
+const AsyncFunction = Object.getPrototypeOf(async function() {}).constructor;
+
+function processData(result, stream, callback) {
+  if (result !== undefined) {
+    if (result instanceof Array) {
+      result.forEach(value => value !== undefined && stream.push(value));
+    } else {
+      stream.push(result);
+    }
+  }
+  callback && callback();
+}
+
+class Chain extends EventEmitter {
+  constructor(fns, skipEvents) {
+    super();
+
+    if (!(fns instanceof Array) || !fns.length) {
+      throw Error("Chain's argument should be a non-empty array.");
+    }
+
+    this.streams = fns.map((fn, index) => {
+      let transform;
+      if (fn instanceof AsyncFunction) {
+        transform = function(chunk, encoding, callback) {
+          fn.call(this, chunk, encoding).then(result => processData(result, this, callback), error => callback(error));
+        };
+      } else if (fn instanceof GeneratorFunction) {
+        transform = function(chunk, encoding, callback) {
+          try {
+            const generator = fn(chunk, encoding);
+            while (true) {
+              const result = generator.next();
+              processData(result.value, this);
+              if (result.done) break;
+            }
+            callback();
+          } catch (error) {
+            callback(error);
+          }
+        };
+      } else if (typeof fn === 'function') {
+        transform = function(chunk, encoding, callback) {
+          try {
+            const result = fn.call(this, chunk, encoding);
+            processData(result, this, callback);
+          } catch (error) {
+            callback(error);
+          }
+        };
+      } else {
+        throw Error('Arguments should be functions.');
+      }
+      const stream = new Transform({objectMode: true, transform});
+      !skipEvents && stream.on('error', error => this.emit('error', error));
+      return stream;
+    });
+    this.input = this.streams[0];
+    this.output = this.streams.reduce((output, stream) => (output && output.pipe(stream)) || stream);
+
+    // connect events
+    if (!skipEvents) {
+      this.output.on('data', item => this.emit('data', item));
+      this.output.on('end', () => this.emit('end'));
+    }
+  }
+}
+
+module.exports = Chain;