diff --git a/README.md b/README.md
index 5726f26..99ad66f 100644
--- a/README.md
+++ b/README.md
@@ -96,11 +96,11 @@ All Configurations
 -----
 ```javascript
 tracker.push({
-  endpoint: '/ENDPOINT', // endpoint to send tracking data to
-  sendCaughtExceptions: true/false, // send exceptions caught by browser. DEFAULT: true
-  attachClientContext: true/false, // attach various client context, such as useragent, platform, and page url. DEFAULT: true
-  sessionId: 'SESSION_ID', // explicitly set a session id
-  devMode: true/false // toggle dev mode. If enabled, outgoing requests are blocked and logged for debugging instead. DEFAULT: false
+  endpoint: '/ENDPOINT', // Endpoint to send tracking data to
+  sendCaughtExceptions: true/false, // Send exceptions caught by browser. DEFAULT: true
+  attachClientContext: true/false, // Attach various client context, such as useragent, platform, and page url. DEFAULT: true
+  sessionId: 'SESSION_ID', // Explicitly set a session id
+  devMode: true/false // Toggle dev mode. If enabled, outgoing requests are blocked and logged for debugging instead. DEFAULT: false
 });
 ```
 
@@ -203,7 +203,7 @@ tracker.push({
 
 Bugs, feature requests, & contributing
 -----
-If you found a bug or want to request a feature, [create a new issue](https://github.com/codeniko/simple-tracker/issues). Contributions are more than welcome :)
+If you found a bug or want to request a feature, [create a new issue](https://github.com/codeniko/simple-tracker/issues). Contributions via pull requests are more than welcome :)
 
 Running unit tests and code coverage
 ----------
diff --git a/dist/simple-tracker.min.js b/dist/simple-tracker.min.js
index 39b5127..d9b81d3 100644
--- a/dist/simple-tracker.min.js
+++ b/dist/simple-tracker.min.js
@@ -1,2 +1,2 @@
-!function(){"use strict";function e(e,t){function n(e){return e?(e^16*Math.random()>>e/4).toString(16):([1e7]+-1e3+-4e3+-8e3+-1e11).replace(/[018]/g,n)}function o(t){var n=e.onerror;e.onerror=function(){t.apply(f,arguments),"function"==typeof n&&n.apply(e,arguments)}}function i(){return p||(p={url:e.location.href,userAgent:e.navigator.userAgent||null,platform:e.navigator.platform||null}),p}function r(){var e=t.cookie,n=e.indexOf(g);if(n>=0){var o=e.indexOf(";",n+1);return o=o<0?e.length:o,e.slice(n+v,o)}}function s(e){t.cookie=g+"="+e}function a(e){s(u=e||u||r()||n())}function c(t){if(d&&Object.keys(t).length>0)if(t.sessionId=u,m&&(t.context=i()),w)console.debug("SimpleTracker: POST "+d,t);else try{var n=new e.XMLHttpRequest;n.open("POST",d,!0),n.setRequestHeader("Content-Type","application/json"),n.send(JSON.stringify(t))}catch(n){e.console&&"function"==typeof e.console.log&&(console.log("Failed to send tracking request because of this exception:\n"+n),console.log("Failed tracking data:",t))}}function l(){}var d,u,f,p,g="trcksesh",v=g.length+1,h=!0,m=!0,w=!1,x={};l.prototype={onerror:function(e,t,n,o,i){var r={message:e,lineno:n,colno:o,stack:i?i.stack:"n/a"};this.logException(r)},logEvent:function(e){this.push({type:"event",event:e})},logException:function(e){this.push({level:"error",type:"exception",exception:e})},logMessage:function(e,t){var n={type:"message",message:e};t&&(n.level=t),this.push(n)},logMetric:function(e,t){this.push({type:"metric",metric:e,value:t})},startTimer:function(t){var n=e.performance;n.now?(x[t]&&console.warn("Timing metric '"+t+"' already started"),console.debug("timer started for:",t),x[t]=n.now()):console.warn("window.performance is not defined")},stopTimer:function(t){var n=e.performance;if(n.now){var o=n.now(),i=x[t];if(void 0!==i){var r=Math.round(o-i);x[t]=void 0,console.debug("timer stopped for:",t,"time="+r),this.logMetric(t,r)}else console.warn("Timing metric '"+t+"' wasn't started")}},push:function(e){var t=typeof e;if("object"===t||"string"===t){if("string"===t)e={text:e};else if(void 0!==e.devMode&&(w=!!e.devMode,delete e.devMode),void 0!==e.attachClientContext&&(m=!!e.attachClientContext,delete e.attachClientContext),e.sessionId&&(a(e.sessionId),delete e.sessionId),e.endpoint&&(u||a(),d=e.endpoint,delete e.endpoint),void 0!==e.sendCaughtExceptions){var n=!!e.sendCaughtExceptions;h=n,n&&o(this.onerror),delete e.sendCaughtExceptions}c(e)}}};var y=e.tracker;if(y&&y instanceof l)f=y;else if(y&&y.length){f=new l;var k=0,C=y.length;for(k=0;k<C;k++)f.push(y[k])}else f=new l;return e.tracker=f,e.SimpleTracker=l,f}var t="undefined"!=typeof module&&module.exports;if("undefined"!=typeof window){var n=e(window,window.document);t&&(e.default=n,module.exports=n)}else{if(!t)throw new Error("");e.default=e,module.exports=e}}();
+!function(){"use strict";function e(e){function t(e){return e?(e^16*Math.random()>>e/4).toString(16):([1e7]+-1e3+-4e3+-8e3+-1e11).replace(/[018]/g,t)}function n(t){var n=e.onerror;e.onerror=function(){t.apply(d,arguments),"function"==typeof n&&n.apply(e,arguments)}}function o(){return f||(f={url:e.location.href,userAgent:e.navigator.userAgent||null,platform:e.navigator.platform||null}),f}function r(){var e=g.cookie,t=e.indexOf(p);if(t>=0){var n=e.indexOf(";",t+1);return n=n<0?e.length:n,e.slice(t+v,n)}}function i(e){g.cookie=p+"="+e}function s(e){i(u=e||u||r()||t())}function a(t){if(l&&Object.keys(t).length>0)if(t.sessionId=u,m&&(t.context=o()),x)console.debug("SimpleTracker: POST "+l,t);else try{var n=new e.XMLHttpRequest;n.open("POST",l,!0),n.setRequestHeader("Content-Type","application/json"),n.send(JSON.stringify(t))}catch(e){}}function c(){}var l,u,d,f,p="trcksesh",v=p.length+1,g=e.document,h=!0,m=!0,x=!1,w={};c.prototype={onerror:function(e,t,n,o,r){var i={message:e,lineno:n,colno:o,stack:r?r.stack:"n/a"};this.logException(i)},logEvent:function(e){this.push({type:"event",event:e})},logException:function(e){this.push({level:"error",type:"exception",exception:e})},logMessage:function(e,t){var n={type:"message",message:e};t&&(n.level=t),this.push(n)},logMetric:function(e,t){this.push({type:"metric",metric:e,value:t})},startTimer:function(t){var n=e.performance;n.now&&(w[t]&&x&&console.warn("Timing metric '"+t+"' already started"),x&&console.debug("timer started for:",t),w[t]=n.now())},stopTimer:function(t){var n=e.performance;if(n.now){var o=n.now(),r=w[t];if(void 0!==r){var i=Math.round(o-r);w[t]=void 0,x&&console.debug("timer stopped for:",t,"time="+i),this.logMetric(t,i)}else x&&console.warn("Timing metric '"+t+"' wasn't started")}},push:function(e){var t=typeof e;if("object"===t||"string"===t){if("string"===t)e={text:e};else if(void 0!==e.devMode&&(x=!!e.devMode,delete e.devMode),void 0!==e.attachClientContext&&(m=!!e.attachClientContext,delete e.attachClientContext),e.sessionId&&(s(e.sessionId),delete e.sessionId),e.endpoint&&(u||s(),l=e.endpoint,delete e.endpoint),void 0!==e.sendCaughtExceptions){var o=!!e.sendCaughtExceptions;h=o,o&&n(this.onerror),delete e.sendCaughtExceptions}a(e)}}};var y=e.tracker;if(y&&y.length){d=new c;var k=0,C=y.length;for(k=0;k<C;k++)d.push(y[k])}else d=new c;return e.tracker=d,e.SimpleTracker=c,d}var t="undefined"!=typeof module&&module.exports;if("undefined"!=typeof window){var n=e(window);t&&(e.default=n,module.exports=n)}else{if(!t)throw new Error("");e.default=e,module.exports=e}}();
 //# sourceMappingURL=simple-tracker.min.map
\ No newline at end of file
diff --git a/dist/simple-tracker.min.map b/dist/simple-tracker.min.map
index d79efbd..3ab84ed 100644
--- a/dist/simple-tracker.min.map
+++ b/dist/simple-tracker.min.map
@@ -1 +1 @@
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\ No newline at end of file
+{"version":3,"sources":["../index.js"],"names":["simpleTracker","window","uuidv4","a","Math","random","toString","replace","setOnError","f","_onerror","onerror","apply","tracker","arguments","getClientContext","clientContext","url","location","href","userAgent","navigator","platform","readCookie","cookie","document","i","indexOf","SESSION_KEY","end","length","slice","SESSION_KEY_LENGTH","setCookie","value","setSession","newSessionId","sessionId","track","data","endpoint","Object","keys","attachClientContext","context","devMode","console","debug","xmlHttp","XMLHttpRequest","open","setRequestHeader","send","JSON","stringify","ex","SimpleTracker","sendCaughtExceptions","timer","prototype","msg","line","col","err","exception","message","lineno","colno","stack","this","logException","logEvent","event","push","type","level","logMessage","logMetric","metric","startTimer","performance","now","warn","stopTimer","stopTime","startTime","undefined","diff","round","text","shouldSend","existingTracker","isModule","module","exports","default","Error"],"mappings":"CAMA,WACE,aAEA,SAASA,EAAcC,GAcrB,SAASC,EAAOC,GACd,OAAOA,GAAGA,EAAgB,GAAdC,KAAKC,UAAaF,EAAE,GAAGG,SAAS,MAAM,MAAM,KAAK,KAAK,KAAK,MAAMC,QAAQ,SAASL,GAIhG,SAASM,EAAWC,GAClB,IAAIC,EAAWT,EAAOU,QAEtBV,EAAOU,QAAU,WACfF,EAAEG,MAAMC,EAASC,WACO,mBAAbJ,GACTA,EAASE,MAAMX,EAAQa,YAK7B,SAASC,IASP,OAPKC,IACHA,GACEC,IAAKhB,EAAOiB,SAASC,KACrBC,UAAWnB,EAAOoB,UAAUD,WAAa,KACzCE,SAAUrB,EAAOoB,UAAUC,UAAY,OAGpCN,EAGT,SAASO,IACP,IAAIC,EAASC,EAASD,OAClBE,EAAIF,EAAOG,QAAQC,GACvB,GAAIF,GAAK,EAAG,CACV,IAAIG,EAAML,EAAOG,QAAQ,IAAKD,EAAI,GAElC,OADAG,EAAMA,EAAM,EAAIL,EAAOM,OAASD,EACzBL,EAAOO,MAAML,EAAIM,EAAoBH,IAIhD,SAASI,EAAUC,GACjBT,EAASD,OAASI,EAAc,IAAMM,EAGxC,SAASC,EAAWC,GAElBH,EADAI,EAAYD,GAAgBC,GAAad,KAAgBrB,KAI3D,SAASoC,EAAMC,GACb,GAAIC,GAAYC,OAAOC,KAAKH,GAAMT,OAAS,EAMzC,GALAS,EAAKF,UAAYA,EACbM,IACFJ,EAAKK,QAAU7B,KAGZ8B,EASHC,QAAQC,MAAM,uBAAyBP,EAAUD,QARjD,IAEE,IAAIS,EAAU,IAAI/C,EAAOgD,eACzBD,EAAQE,KAAK,OAAQV,GAAU,GAC/BQ,EAAQG,iBAAiB,eAAgB,oBACzCH,EAAQI,KAAKC,KAAKC,UAAUf,IAC5B,MAAMgB,KAOd,SAASC,KAjFT,IAOIhB,EACAH,EACAxB,EAEAG,EAXAY,EAAc,WACdI,EAAqBJ,EAAYE,OAAS,EAE1CL,EAAWxB,EAAOwB,SAClBgC,GAAuB,EACvBd,GAAsB,EACtBE,GAAU,EAIVa,KAyEJF,EAAcG,WAGZhD,QAAS,SAASiD,EAAK3C,EAAK4C,EAAMC,EAAKC,GACrC,IAAIC,GACFC,QAASL,EACTM,OAAQL,EACRM,MAAOL,EACPM,MAAOL,EAAMA,EAAIK,MAAQ,OAG3BC,KAAKC,aAAaN,IAGpBO,SAAU,SAASC,GACjBH,KAAKI,MACHC,KAAM,QACNF,MAAOA,KAIXF,aAAc,SAASN,GACrBK,KAAKI,MACHE,MAAO,QACPD,KAAM,YACNV,UAAWA,KAIfY,WAAY,SAASX,EAASU,GAC5B,IAAIpC,GACFmC,KAAM,UACNT,QAASA,GAIPU,IACFpC,EAAKoC,MAAQA,GAGfN,KAAKI,KAAKlC,IAGZsC,UAAW,SAASC,EAAQ5C,GAC1BmC,KAAKI,MACHC,KAAM,SACNI,OAAQA,EACR5C,MAAOA,KAIX6C,WAAY,SAASD,GACnB,IAAIE,EAAc/E,EAAO+E,YACrBA,EAAYC,MAEVvB,EAAMoB,IAAWjC,GACnBC,QAAQoC,KAAK,kBAAoBJ,EAAS,qBAE5CjC,GAAWC,QAAQC,MAAM,qBAAsB+B,GAC/CpB,EAAMoB,GAAUE,EAAYC,QAIhCE,UAAW,SAASL,GAClB,IAAIE,EAAc/E,EAAO+E,YACzB,GAAIA,EAAYC,IAAK,CACnB,IAAIG,EAAWJ,EAAYC,MACvBI,EAAY3B,EAAMoB,GAEtB,QAAkBQ,IAAdD,EAAyB,CAC3B,IAAIE,EAAOnF,KAAKoF,MAAMJ,EAAWC,GACjC3B,EAAMoB,QAAUQ,EAChBzC,GAAWC,QAAQC,MAAM,qBAAsB+B,EAAQ,QAAUS,GACjElB,KAAKQ,UAAUC,EAAQS,QAEvB1C,GAAWC,QAAQoC,KAAK,kBAAoBJ,EAAS,sBAK3DL,KAAM,SAASlC,GACb,IAAImC,SAAcnC,EAElB,GAAa,WAATmC,GAA8B,WAATA,EAAzB,CAIA,GAAa,WAATA,EACFnC,GACEkD,KAAMlD,QA4BR,QAxBqB+C,IAAjB/C,EAAKM,UACPA,IAAYN,EAAKM,eACVN,EAAKM,cAGmByC,IAA7B/C,EAAKI,sBACPA,IAAwBJ,EAAKI,2BACtBJ,EAAKI,qBAGVJ,EAAKF,YACPF,EAAWI,EAAKF,kBACTE,EAAKF,WAGVE,EAAKC,WAEFH,GACHF,IAEFK,EAAWD,EAAKC,gBACTD,EAAKC,eAGoB8C,IAA9B/C,EAAKkB,qBAAoC,CAC3C,IAAIiC,IAAenD,EAAKkB,qBACxBA,EAAuBiC,EACnBA,GACFlF,EAAW6D,KAAK1D,gBAEX4B,EAAKkB,qBAIhBnB,EAAMC,MAIV,IAAIoD,EAAkB1F,EAAOY,QAE7B,GAAI8E,GAAmBA,EAAgB7D,OAAQ,CAE7CjB,EAAU,IAAI2C,EACd,IAAI9B,EAAI,EACJI,EAAS6D,EAAgB7D,OAC7B,IAAKJ,EAAI,EAAGA,EAAII,EAAQJ,IACtBb,EAAQ4D,KAAKkB,EAAgBjE,SAG/Bb,EAAU,IAAI2C,EAKhB,OAFAvD,EAAOY,QAAUA,EACjBZ,EAAOuD,cAAgBA,EAChB3C,EAGT,IAAI+E,EAA6B,oBAAXC,QAA0BA,OAAOC,QAEvD,GAAsB,oBAAX7F,OAAwB,CACjC,IAAIY,EAAUb,EAAcC,QACxB2F,IACF5F,EAAc+F,QAAUlF,EACxBgF,OAAOC,QAAUjF,OAEd,CAAA,IAAI+E,EAKT,MAAM,IAAII,MAAM,IAHhBhG,EAAc+F,QAAU/F,EACxB6F,OAAOC,QAAU9F,GAxPrB","file":"simple-tracker.min.js"}
\ No newline at end of file
diff --git a/index.js b/index.js
index 9e45742..b33c38b 100644
--- a/index.js
+++ b/index.js
@@ -7,10 +7,11 @@
 (function() {
   'use strict'
 
-  function simpleTracker(window, document) {
+  function simpleTracker(window) {
     var SESSION_KEY = 'trcksesh'
     var SESSION_KEY_LENGTH = SESSION_KEY.length + 1
 
+    var document = window.document
     var sendCaughtExceptions = true
     var attachClientContext = true
     var devMode = false
@@ -81,12 +82,7 @@
             xmlHttp.open('POST', endpoint, true) // true for async
             xmlHttp.setRequestHeader('Content-Type', 'application/json')
             xmlHttp.send(JSON.stringify(data))
-          } catch(ex) {
-            if (window.console && typeof window.console.log === 'function') {
-              console.log('Failed to send tracking request because of this exception:\n' + ex)
-              console.log('Failed tracking data:', data)
-            }
-          }
+          } catch(ex) { }
         } else {
           console.debug('SimpleTracker: POST ' + endpoint, data)
         }
@@ -149,13 +145,12 @@
       startTimer: function(metric) {
         var performance = window.performance
         if (performance.now) {
-          if (timer[metric]) {
+          /* istanbul ignore if */
+          if (timer[metric] && devMode) {
             console.warn("Timing metric '" + metric + "' already started")
           }
-          console.debug('timer started for:', metric)
+          devMode && console.debug('timer started for:', metric)
           timer[metric] = performance.now()
-        } else {
-          console.warn('window.performance is not defined')
         }
       },
 
@@ -164,13 +159,14 @@
         if (performance.now) {
           var stopTime = performance.now()
           var startTime = timer[metric]
+          /* istanbul ignore else */
           if (startTime !== undefined) {
             var diff = Math.round(stopTime - startTime)
             timer[metric] = undefined
-            console.debug('timer stopped for:', metric, 'time=' + diff)
+            devMode && console.debug('timer stopped for:', metric, 'time=' + diff)
             this.logMetric(metric, diff)
           } else {
-            console.warn("Timing metric '" + metric + "' wasn't started")
+            devMode && console.warn("Timing metric '" + metric + "' wasn't started")
           }
         }
       },
@@ -228,10 +224,7 @@
 
     var existingTracker = window.tracker // either instance of SimpleTracker or existing array of events to log that were added while this script was being loaded asyncronously
 
-    // reuse SimpleTracker instance if already created
-    if (existingTracker && existingTracker instanceof SimpleTracker) {
-      tracker = existingTracker
-    } else if (existingTracker && existingTracker.length) {
+    if (existingTracker && existingTracker.length) {
       // move all from existing and push into our tracker object
       tracker = new SimpleTracker()
       var i = 0
@@ -248,10 +241,10 @@
     return tracker
   }
 
-
   var isModule = typeof module !== 'undefined' && module.exports
+  /* istanbul ignore else */
   if (typeof window !== 'undefined') {
-    var tracker = simpleTracker(window, window.document) // sets window.tracker
+    var tracker = simpleTracker(window) // sets window.tracker
     if (isModule) {
       simpleTracker.default = tracker
       module.exports = tracker
diff --git a/test/unit/simple-tracker.js b/test/unit/simple-tracker.js
index 9e59cf9..f835a4b 100644
--- a/test/unit/simple-tracker.js
+++ b/test/unit/simple-tracker.js
@@ -2,6 +2,7 @@
 
 const assert = require('chai').assert
 const sinon = require('sinon')
+const rewire = require('rewire')
 
 const simpleTracker = require('../../index.js')
 
@@ -40,7 +41,11 @@ describe('simple-tracker', function() {
 
   function reset() {
     onerrorSpy = sinon.spy()
+    document = {
+      cookie: '',
+    }
     window = {
+      document,
       XMLHttpRequest: MockXMLHttpRequest,
       location: {
         href: mockHref,
@@ -54,10 +59,7 @@ describe('simple-tracker', function() {
         now: sinon.stub(),
       }
     }
-    document = {
-      cookie: '',
-    }
-    simpleTracker(window, document) // sets tracker to window object
+    simpleTracker(window) // sets tracker to window object
     mockRequest = sinon.createStubInstance(MockXMLHttpRequest)
     sinon.stub(window, 'XMLHttpRequest').returns(mockRequest)
     tracker = window.tracker
@@ -307,7 +309,7 @@ describe('simple-tracker', function() {
     assert.isTrue(mockRequest.send.notCalled)
 
     // let's load our tracker
-    simpleTracker(window, document)
+    simpleTracker(window)
 
     assert.isTrue(mockRequest.open.calledTwice)
     assert.isTrue(mockRequest.send.calledTwice)
@@ -415,7 +417,7 @@ describe('simple-tracker', function() {
     })
 
     // second load, same window obj
-    simpleTracker(window, document)
+    simpleTracker(window)
     tracker.push({ mockData2 })
 
     assert.isTrue(mockRequest.open.calledTwice)
@@ -443,4 +445,31 @@ describe('simple-tracker', function() {
     done()
   })
 
+  it('should auto initialize with window object if one exists', function(done) {
+    delete window.tracker // ensure no instance of tracker loaded
+    delete window.SimpleTracker
+    global.window = window
+
+    assert.isUndefined(window.tracker)
+    assert.isUndefined(window.SimpleTracker)
+
+    // window object is now in global, so should be picked up automatically
+    const rTracker = rewire('../../index.js') // rewire loads fresh instance of module
+
+    assert.isDefined(window.SimpleTracker)
+    assert.instanceOf(window.tracker, window.SimpleTracker)
+    assert.instanceOf(rTracker, window.SimpleTracker)
+
+    delete global.window // cleanup
+
+    done()
+  })
+
+  it('dont do anything if data pushed is not an object or string', function(done) {
+    tracker.push(() => {})
+    assert.isTrue(mockRequest.open.notCalled)
+    assert.isTrue(mockRequest.send.notCalled)
+    done()
+  })
+
 })