diff --git a/types/slimerjs/index.d.ts b/types/slimerjs/index.d.ts
index b45d6d9495..327f2ac4b8 100644
--- a/types/slimerjs/index.d.ts
+++ b/types/slimerjs/index.d.ts
@@ -112,14 +112,14 @@ interface IWebPage {
     // evaluate<T1, T2, T3, R>(callback: (arg1: T1, arg2: T2, arg3: T3) => R, arg1: T1, arg2: T2, arg3: T3): Promise<R>;
     // evaluate<R>(callback: (...args: any[]) => R, ...args: any[]): Promise<R>;
     evaluate<R>(callback: () => R, ...args: any[]): R;
-    evaluateAsync(fn: Function): void;
+    evaluateAsync(fn: () => void): void;
     evaluateJavaScript(str: string): any; // :TODO: elaborate this when documentation improves
     getPage(windowName: string): IWebPage;
     go(index: number): void;
     goBack(): void;
     goForward(): void;
     includeJs(url: string): Promise<void>;
-    includeJs(url: string, callback: Function): void;
+    includeJs(url: string, callback: () => void): void;
     injectJs(filename: string): Promise<boolean>;
     injectJs(filename: string): boolean;
     open(url: string): Promise<string>;
@@ -153,7 +153,7 @@ interface IWebPage {
 
     // Callbacks
     onAlert: (msg: string) => any;
-    onCallback: Function;  // EXPERIMENTAL
+    onCallback: () => void;  // EXPERIMENTAL
     onClosing: (closingPage: IWebPage) => any;
     onConfirm: (msg: string) => boolean;
     onConsoleMessage: (msg: string, lineNum?: number, sourceId?: string) => any;
diff --git a/types/slimerjs/slimerjs-tests.ts b/types/slimerjs/slimerjs-tests.ts
index f3de79d963..3e11b5174b 100644
--- a/types/slimerjs/slimerjs-tests.ts
+++ b/types/slimerjs/slimerjs-tests.ts
@@ -5,18 +5,18 @@ let vUrl = 'https://www.w3c.org';
 let vUserAgent = 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_3) AppleWebKit/602.4.8 (KHTML, like Gecko) Version/10.0.3 Safari/602.4.8'
 page.settings.userAgent = vUserAgent;
 
-page.onConsoleMessage = function(vMsg) {
+page.onConsoleMessage = (vMsg) => {
 };
 
-page.onAlert = function(vMsg) {
+page.onAlert = (vMsg) => {
 };
 
-page.onLoadStarted = function() {
+page.onLoadStarted = () => {
 };
 
 page.captureContent = [ /json/ ]
 
-page.onResourceReceived = function(oResponse) {
+page.onResourceReceived = (oResponse) => {
   oResponse.id;
   oResponse.bodySize;
   oResponse.body;
@@ -24,7 +24,7 @@ page.onResourceReceived = function(oResponse) {
   oResponse.headers;
 };
 
-page.onResourceRequested = function(oRequestData, oNetworkRequest) {
+page.onResourceRequested = (oRequestData, oNetworkRequest) => {
   oRequestData.headers;
   oRequestData.id;
   oRequestData.method;
@@ -33,31 +33,31 @@ page.onResourceRequested = function(oRequestData, oNetworkRequest) {
 };
 
 
-page.onLoadFinished = function(vStatus) {
+page.onLoadFinished = (vStatus) => {
   phantom.exit();
 };
 
-page.onInitialized = function() {
+page.onInitialized = () => {
 };
 
-page.onPageCreated = function(oPage) {
+page.onPageCreated = (oPage) => {
   let oCookie: ICookie
   oPage.addCookie(oCookie);
 };
 
 
 page.open(vUrl) // loads a page
-  .then(function(){ // executed after loading
-    page.viewportSize = { width:414, height:736 };
+  .then(() => { // executed after loading
+    page.viewportSize = { width: 414, height: 736 };
 
 
     let vFilename = `../data/page01.png`;
-    page.render(vFilename, {onlyViewport:true})
+    page.render(vFilename, {onlyViewport: true})
 
     // then open a second page
     return page.open('http://');
   })
-  .then(function(){
+  .then(() => {
     // click somewhere on the second page
     page.sendEvent("click", 5, 5, 'left', 0);
     slimer.exit()