The hterm.js code will initialize defaults for the various objects. You can override them yourself (such as setting up hterm.defaultStorage) before you instantiate anything.
An hterm.Terminal instance is created and initialization code attached to onTerminalReady. That callback creates a new hterm.Terminal.IO object by calling this.io.push, and then binding its callbacks. Finally the terminal is attached to the DOM via a call to decorate. The terminal is now ready to accept data.
In order for the terminal itself to handle keyboard shortcuts and such, a call to installKeyboard is made. This binds all the relevant input callbacks to be captured by hterm. It will handle things like pressing “X” and “Ctrl+X” and sending the resulting data to the IO object.
At this point, all data runs through the IO object created earlier. When the user inputs text (typing on the keyboard, pasting, etc...), the IO callbacks are called such as sendString and onVTKeystroke. The data is then sent to the remote process (via network socket/whatever). When new data is available from the remote process, it is passed to the IO object via the print or println functions. The logic to communicate with the remote process is left entirely in the hands of the developer and is outside the scope of hterm.
Drilling down a bit, user input is processed first by hterm.Keyboard. It looks up the keypress in hterm.Keyboard.KeyMap (for the default action), and the keybindings in hterm.Keyboard.Bindings (for user/custom actions). The resolved action is then performed. If it expands into text (as most do), it is sent to the IO object callbacks (sendString and onVTKeystroke). Or it might trigger an action in which case it is called.
When data is printed to the IO object, it is sent to the terminal's VT layer to be interpreted (control sequences and such).
As new lines are generated in the VT layer, they‘re sent to hterm.Terminal which adds to the active hterm.Screen, and any excess lines are moved to the terminal’s scrollback. When the user scrolls the output, hterm.ScrollPort loads rows on the fly from hterm.Terminal (as a “RowProvider”).
