If you type § (section sign) followed by cmd:op [yourname] inside a sign or book, certain unpatched servers will execute the command as console.

He typed:

The strongest selling point of Eaglercraft is right in the name: Unlike the official Minecraft Classic or the downloadable client, Eaglercraft runs entirely within a web browser without requiring external files or admin privileges.

While Eaglercraft aims for a faithful 1.5.2 or 1.8.8 experience, its browser-based nature allows for unique interactions: The "Invincibility" Glitch