Make ES5-compatible again as requested in #21

.jshintrc

@@ -1,7 +1,7 @@
 {
 	"node": true, // Enable globals available when code is running inside of the NodeJS runtime environment.
 	"browser": true, // Standard browser globals e.g. `window`, `document`.
-	"esversion": 6, // Allow ES.next specific features such as `const` and `let`.
+	"esversion": 5,
 	"bitwise": false, // Prohibit bitwise operators (&, |, ^, etc.).
 	"camelcase": false, // Permit only camelcase for `var` and `object indexes`.
 	"curly": false, // Require {} for every new block or scope.

gruntfile.js

@@ -4,7 +4,7 @@ module.exports = function(grunt) {
 	// Unified Watch Object
 	var watchFiles = {
 		libJS: ['gruntfile.js', 'index.js', 'lib/**/*.js'],
-		testJS: ['test/**/*.js'],
+		testJS: ['test/**/*.js']
 	};
 
 	// Project Configuration
@@ -40,7 +40,7 @@ module.exports = function(grunt) {
 					timeout: 5000,
 					noFail: false
 				}
-			},
+			}
 		}
 	});
 

lib/index.js

@@ -1,16 +1,66 @@
 'use strict';
 
+// Small Map polyfill to remain ES5-compatible as requested in issue #21 while also solving PR #30
+
+var MapPolyfill = function () {
+	this.elements = [];
+	this.size = 0;
+};
+
+MapPolyfill.prototype.has = function (key) {
+	var i;
+	for (i = 0; i < this.elements.length; ++i) {
+		if (this.elements[i].key === key) {
+			return true;
+		}
+	}
+	return false;
+};
+
+MapPolyfill.prototype.get = function (key) {
+	var i;
+	for (i = 0; i < this.elements.length; ++i) {
+		if (this.elements[i].key === key) {
+			return this.elements[i].value;
+		}
+	}
+	return false;
+};
+
+MapPolyfill.prototype.set = function (key, value) {
+	var i;
+	for (i = 0; i < this.elements.length; ++i) {
+		if (this.elements[i].key === key) {
+			this.elements[i].value = value;
+			return;
+		}
+	}
+	this.elements.push({ key: key, value: value });
+	this.size++;
+};
+
+MapPolyfill.prototype.delete = function (key) {
+	var i;
+	for (i = 0; i < this.elements.length; ++i) {
+		if (this.elements[i].key === key) {
+			this.elements.splice(i, 1);
+			this.size--;
+			return;
+		}
+	}
+};
+
 var AsyncLock = function (opts) {
 	opts = opts || {};
 
 	this.Promise = opts.Promise || Promise;
 
 	// format: {key : [fn, fn]}
 	// queues.has(key) indicates job running for key
-	this.queues = new Map();
+	this.queues = new MapPolyfill();
 
 	// domain of current running func {key : fn}
-	this.domains = new Map();
+	this.domains = new MapPolyfill();
 
 	// lock is reentrant for same domain
 	this.domainReentrant = opts.domainReentrant || false;
@@ -252,4 +302,4 @@ AsyncLock.prototype._promiseTry = function(fn) {
 	}
 };
 
-module.exports = AsyncLock;
+module.exports = AsyncLock;