Data is expensive

• Proxy browsers preferred (Opera Mini, UCBrowser)
• Site served != Site received
• Your Javascript may not make
  it to the browser

Speeds are low

• Sites built for high-speed broadband will slow down on 3G and possibly hang on 2G
• Remember                                                 ?

Devices aren't as powerful

Legacy and low performance devices (Feature phones, older smartphones etc.)

Architecture

Progressive enhancement

• These are Connectivity independent, safe and installable applications
• Universal Javascript is the future

Write CSS and JS keeping Proxy Browsers in mind

• Opera mini will rip out your styles
• Your large JS scripts will be killed
• Opera doesn't support all events

Adaptive Development

• This uses static layouts based on breakpoints which don’t respond once they’re initially loaded.

• Not ideal, but if push comes to shove and you need your app to work on a feature phone, you might need to serve out a different page altogether

Server Side Rendering when possible

• Sometimes, you don’t need Single Page Applications. A simple server rendered static website would do.
• Static sites work across browsers, network conditions, geographies and require little to no Javascript. If you can make do with one, then your work is cut out for you.

Development

Develop mobile first 

• It always helps with perf

Follow Best Practices

• Trim, Bundle, GZIP and Tree Shake your code to make it lean.

QA

Test on

• Real Devices
• Real Networks

Prioritise Perf Monitoring

• Performance should be constantly monitored, and performance bugs should be seen as at par with others.
• Performance Sprints between regular development cycles

Tools everywhere - Use them!

• NewRelic
• DynaTrace
• Lighthouse for PWAs

What?

• Shared execution on client and server
• Server-side rendering

Why?

• Works on JS and non-JS browsers
• Renders HTML instead of empty shell + JS (SPA)
• Snappy performance

How?

• Run your f/w on the server and client
• React Universal
• Angular Universal
• Ember Fastboot