Website testing has become increasingly complex. The days of checking functionality in a couple of browsers are long gone. Your latest masterpiece must be rigorously evaluated on a range of mobile, tablet and desktop devices with differing OSs, screen resolutions, and capabilities. In extreme cases, it could take as long as the original development.
The process is complicated further by touch-screens, hybrid devices, and high-density displays. If you’re coding on a regular PC with a mouse and keyboard, it’s difficult to appreciate how your masterpiece will operate. Features such as mouse hover won’t necessarily work and your application could be inoperable. But how can you test your system during development and avoid the pain of managing and switching between multiple devices?
Fortunately, all modern browsers offer mobile emulation tools, and one of the best can be found in Chrome. It can help identify early problems without leaving the comfort of your PC and development environment.
Start Chrome, navigate to the web page you want to test and open the Developer Tools (Menu > Tools > Developer Tools, Cmd + Opt + I on macOS or F12 / Ctrl + Shift + I on Windows and Linux).
You can now enable the browser emulator by clicking the Toggle device toolbar icon in the top left:
A device simulation will now appear:
The dimensions of the emulated screen can be changed when Responsive is selected as the device type.
Touch Enabled Emulation
touchend. Mouse-specific events and CSS effects should not occur.
Hold down Shift then click and move your mouse to emulate pinch zooming.
The Mobile Emulator Device Toolbar
It’s worth spending a little time familiarizing yourself with the toolbar and menu above the mobile emulator:
The default controls are:
- the device type (or Responsive)
- the current resolution
- the scale (the screen can be zoomed in or out to fit better in the emulator pane)
- the network speed
- a portrait/landscape toggle button
The three-dot menu allows you to show or hide additional controls:
- the device frame (if available, a graphic of the phone or tablet)
- CSS media query bars (see below)
- a pixel ruler
- add device pixel ratios
- add device types
- capture a screenshot (including the device frame if shown)
- capture a full-page screen shot
CSS Media Query Bars
Select Show media queries from the three-dot menu to view a graphical color-coded representation of all media queries set in the CSS.
- BLUE: queries which target a maximum width
- GREEN: queries which target widths within a range
- ORANGE: queries which target a minimum width
Any bar can be clicked to set the emulator screen to that width.
Emulated Device Options
The drop-down menu on the left allows you to select a device. Several dozen presets are provided for popular smart phones and tablets, including iPhones, iPads, Kindles, Nexus tablets, Samsung Galaxy, and so on.
Not all devices are presented at once. Click Edit… at the bottom of the device drop-down or click the DevTools Settings cog icon and choose the Devices tab:
You can enable or disable devices or enter your own by defining:
- a name
- a classification such as “Mobile” or “Tablet”
- a browser user agent string
- the device resolution
- and pixel ratio (such as 2 for iPhone Retina screens where the pixel density is twice as high as the reported viewport resolution)
All browsers identify themselves with a user agent string sent on every HTTP header. This can be examined on the client or server-side and, during the dark days of web development, would be used to modify or provide a different user experience. In extreme cases, the viewer would be directed to a different site. The technique was always flawed but has become largely redundant owing to Responsive Web Design techniques, and it was unsustainable given the number of devices available on the market.
Bandwidth Throttling Simulation
The throttling drop-down allows you to emulate slow network speeds typically experienced on mobile connections or dodgy hotel and airport Wi-Fi! You can use this to ensure your site or application loads quickly and remains responsive in all environments.
The throttling drop-down is available in the Network tab and Chrome’s device toolbar. You can set your own bandwidth configuration by clicking the DevTools Settings cog icon and choosing the Throttling tab:
Click Add custom profile then enter:
- the profile name
- the download speed in kilobits per second
- the upload speed in kilobits per second
- the latency in milliseconds (the typical delay when making a network request)
Emulated Mobile Sensors
Smart phones and tablets often have sensors such as GPS, gyroscopes, and accelerometers, which aren’t normally present in desktop devices. These can be emulated in Chrome by choosing More tools, then Sensors from the Developer Tools main three-dot menu:
A new pane appears which allows you to define:
- The current latitude and longitude or select a major city from the drop-down. You can also select Location unavailable to emulate how your application reacts when the device cannot obtain a reliable GPS signal.
- The orientation. Several presets are available or you can move the device image by clicking and dragging.
- The touch response.
- An idle state to examine how an app reacts to a lock screen.
Remote Real Device Debugging
Finally, Chrome allows you to connect a real Android device via USB for remote device debugging. Enter
Chrome allows you to set up port forwarding so you can navigate to a web address on your local server on the device. Chrome’s preview pane shows a synchronized view of the device screen and you can interact either using the device or Chrome itself.
The full range of developer tools can be used including the Application tab to test Progressive Web Apps in offline mode. Note that, unlike a real application which requires HTTPS, Chrome permits PWAs to run from localhost over an HTTP connection.
Great! I Don’t Need Any Devices Now!
Chrome’s mobile browser emulator is useful and powerful, but it’s no substitute for interacting with your website or app on a real device to evaluate the full user experience.
You should also be aware that no device emulator is perfect. For example, Chrome shows a representation of the page on an iPhone or iPad but will not attempt to simulate the standards support or Safari quirks.
That said, for quick and dirty mobile testing, Chrome’s device emulation is excellent. It’s far easier than switching between real smart phones, and you’ll have all the developer tools at your disposal. It saves hours of effort.
Craig is a freelance UK web consultant who built his first page for IE2.0 in 1995. Since that time he's been advocating standards, accessibility, and best-practice HTML5 techniques. He's created enterprise specifications, websites and online applications for companies and organisations including the UK Parliament, the European Parliament, the Department of Energy & Climate Change, Microsoft, and more. He's written more than 1,000 articles for SitePoint and you can find him @craigbuckler.