using node-gmt

package.json

@@ -32,5 +32,8 @@
     "istanbul": "^0.4.2",
     "mocha": "^3.0.2",
     "sinon": "^1.17.3"
+  },
+  "dependencies": {
+    "node-gmt": "^0.0.1"
   }
 }

src/task.js

@@ -2,7 +2,7 @@
 
 var convertExpression = require('./convert-expression');
 var validatePattern = require('./pattern-validation');
-var tz = require('./timezone/timezone-converter');
+var GMT = require('node-gmt');
 
 module.exports = (function(){
   function matchPattern(pattern, value){
@@ -15,7 +15,7 @@ module.exports = (function(){
 
   function mustRun(task, date){
     if(task.timezone)
-      date = tz.atTimezone(date, task.timezone);
+      date = new GMT(task.timezone).relativeDate(date);
 
     var runInSecond = matchPattern(task.expressions[0], date.getSeconds());
     var runOnMinute = matchPattern(task.expressions[1], date.getMinutes());

test/timezone/task-with-timezone-test.js

@@ -4,13 +4,12 @@ var expect = require('expect.js');
 var sinon = require('sinon');
 var Task = require('../../src/task');
 var cron = require('../../src/node-cron');
-var tz = require('../../src/timezone/timezone-converter')
 
 describe('task at timezone', function () {
     it('should should perform at timezone', function () {
         var task = new Task('* 4 * * *', function () {
             this.executed += 1;
-        }, "America/Virgin");
+        }, "GMT-04:00");
         task.executed = 0;
         var date = new Date('August 19, 2018 00:00:00 GMT-03:00');
         date.setHours(date.getHours() + 1);
@@ -25,7 +24,7 @@ describe('task at timezone', function () {
     describe('by node-cron', function () {
         beforeEach(function () {
             this.now = new Date('August 19, 2018 03:00:00 GMT-04:00');
-            this.clock = sinon.useFakeTimers(this.now);
+            this.clock = sinon.useFakeTimers(this.now.getTime());
         });
 
         afterEach(function () {
@@ -39,7 +38,7 @@ describe('task at timezone', function () {
             var task = cron.schedule('* 4 * * *', function () {
                 executed++;
                 executedAt = new Date();
-            }, true, "America/Virgin");
+            }, true, "GMT-04:00");
 
             this.clock.tick(60 * 60 * 1000);
             this.now.setHours(this.now.getHours() + 1);