What is Opera Mini?

• “Feature phone” (“dumb phone”) browser
  • Runs on most J2ME systems
  • Also available for smart phones and tablets including iOS devices
• Proxy browser or “thin client” browser

Opera Mobile is a standard web browser.

How does it work?

Proxy server does what?

• Renders the CSS and HTML
• Runs the JavaScript
• Returns a snapshot of the page

It’s where the magic happens. Client just displays server rendering.

How JavaScript works in Opera Mini

Scripts run until they complete or until they are paused by the server — whichever comes first.

• setTimeout and setInterval timeout limits:
• Opera Mini 5 & 6: about 5 seconds
• Opera Mini 4: about 2.5 seconds
• XMLHttpRequest timeout limit:
• Opera Mini 5 & 6: 15 seconds
• Opera Mini 4: 8 seconds

When limit is reached: Scripts are paused. Page is returned in its current state.

How JavaScript works in Opera Mini (Part 2)

• setTimeout() and setInterval() usually executed once due to timeouts.

  • Makes delayed loading almost impossible.
  • Makes animation almost impossible.
• onload and onunload run, subject to limits
• No mouseout event
• mouseover is only triggered as part of a 'click' or 'tap' sequence
• No touch events

How JavaScript works in Opera Mini (Part 3)

DOM Changes require a trip to the server.

var p = document.createElement('p');
p.innerHTML = 'HUZZAH!';
button.onclick = function(){ document.body.appendChild(p); }

• Client sends request to the proxy.
• Proxy makes request to page.
• Difference between old state and new state returned to phone.

CSS Support

Presto is Opera's browser engine.

• Mini 5 uses Presto 2.4 engine
• Mini 6 uses Presto 2.5 engine

Puts Mini on par with Opera Desktop 10 support for CSS and HTML — strong CSS and HTML5 support (with caveats)

• Some resource-intensive CSS properties aren’t supported
• Some typographic properties aren’t supported (since most devices have limited fonts).

Ecryption and SSL Support

• Supports encryption between client and proxy
• Supports encryption between proxy and remote SSL-encrypted server
• DOES NOT support encryption from client to remote SSL-encrypted server

Comes down to this: do you trust Opera to be your intermediary?

No support for …

• No support for window.open() and window.close()
• No support for onhashchange event
• No localStorage, sessionStorage, Application Cache or WebSQL
• No geo-location
• No web messaging
• No web workers
• No viewport meta tag support in Opera Mini <= 5 (Mini 6 has it) — use media queries

Remember, this was designed for dumb phones with low power and storage on high-latency (slow) networks.

Links

• A developer’s look at Opera Mini 5
• A developer’s look at Opera Mini 5 beta 2
• For development, download MicroEmulator (requires Java) and Opera Mini (Filename: mini.jad)
• Opera Mini FAQ