Resize `xterm.js` height to fit contents automatically - xtermjs

Question

I'd like to use an xterm.js session that perfectly fits the height of the current contents. So every time a line is added, the size would adjust to fit that new height. The height would never be bigger than it needs to be but a scrollbar would never be shown.
I can't figure out a way to either use the fit plugin to accomplish this or to check the contents of the current xterm.js session to manually resize the row count as needed.

Answer 1

Beside what I wrote in the comment above, you might get away with a simpler solution by doing the following schematically (untested):
const MAX_ROWS = 20; // test upfront, as it depends on font metrics etc.
let visibleRows = 1; // start with one visible row
const term = new Terminal({
// setting scrollback is important to not lose data early
scrollback: MAX_ROWS - visibleRows,
rows: visibleRows,
...
});
// when data comes in, use the write callback to adjust terminal height
term.write(data, () => {
// get current buffer length (visible rows + rows in scrollback)
const bufferLength = term.buffer.active.length;
if (bufferLength > visibleRows) {
// resize will pull scrollback lines back into visible area
// since we have MAX_ROWS in place, bufferLength will never
// exceed your supported area (everything else is discarded)
term.resize(some_cols, bufferLength);
visibleRows = bufferLength;
// adjust scrollback to stay within (MAX_ROWS - visibleRows) constraint
// drops to 0 once we hit MAX_ROWS
term.options.scrollback = MAX_ROWS - bufferLength;
// finally adjust your container height
adjustContainerHeight();
}
});
function adjustContainerHeight() {
// can be implemented by reversing FitAddon.proposeDimensions
// maybe easier: test upfront and do a rows -> px_height mapping
...
}
Downside of this simpler approach - it might give you ugly resizing artifacts during incoming data, esp. the terminal height might jump in between and show a scrollbar for a short amount of time. If thats a showstopper for you - the double terminal approach should avoid the in between jumps and scrollback flickering.
Furthermore both ways rely on term.resize, which might trigger cmdline apps on a real PTY to resend data. This cannot be avoided, the terminal interface is meant to work that way (the application decides that on its own).
Maybe this helps.