Return node version check and include additional v4 engine.

index.js

@@ -1,6 +1,17 @@
 'use strict';
 
+var semver = require('semver');
+var packageData = require('./package.json');
+
+function nodeVersionCheck(version, expected) {
+  if (!semver.satisfies(version, expected)) {
+    throw new Error('Node.js version ' + version + ' is expected to be ' + expected);
+  }
+}
+nodeVersionCheck(process.versions.node, packageData.engines.node);
+
 module.exports = require('./lib');
+module.exports.nodeVersionCheck = nodeVersionCheck;
 module.exports.Node = require('./lib/node');
 module.exports.Transaction = require('./lib/transaction');
 module.exports.Service = require('./lib/service');

package.json

@@ -78,7 +78,7 @@
     "bitcore-p2p": "~1.0.0"
   },
   "engines": {
-    "node": "^0.12"
+    "node": "^0.12 || ^4.2"
   },
   "os": [
     "darwin",