Autoscroll to bottom not working when typing command and output

[DmG-tech]

Xterm version: 4.19.0

Scroll go to top, when i typing and when i get output to console from remote server.
Terminal config:

cursorStyle: "underline",
cursorBlink: true,
theme: xtermjsTheme,
cols: 80,

I try: disableStdin: on|off, rows: count, scrollback: count, macOptionClickForcesSelection: on|off.

I try use terminal:

    function initTerminal() {
        const protocol = "ws://";
        const host = document.location.host;
        const endpoint = contextPath + "/server/" + getServerId();
        const url = protocol + host + endpoint;

        websocket = new WebSocket(url);

        terminal = new Terminal(terminalOption);
        terminal.open(terminalContainer);
        terminal.focus();

        websocket.onmessage = function (data) {
            terminal.clear();
            terminal.write(data.data);
            terminal.scrollLines(99999999);
        };

        terminal.onData(function (data) {
            websocket.send(data);
            terminal.scrollLines(99999999);
        })

        terminal.onBinary(function (data) {
            websocket.send(data);
            terminal.scrollLines(99999999);
        })
    }

I try use - terminal.scrollToBottom() and terminal.scrollLines(99999999) - not working.

I try use:

var block = document.getElementsByClassName('xterm-viewport');
block.scrollTop = block.scrollHeight;

or

var block = document.getElementsByClassName('terminal xterm');
block.scrollTop = block.scrollHeight;

• not working.

I try use terminal with attach addons:

    function initTerminal() {
        const protocol = "ws://";
        const host = document.location.host;
        const endpoint = contextPath + "/server/" + getServerId();
        const url = protocol + host + endpoint;

        websocket = new WebSocket(url);
        websocket.onmessage = function (data) {
            terminal.clear();
        };

        terminal = new Terminal(terminalOption);
        const attachAddon = new AttachAddon.AttachAddon(websocket);
        terminal.loadAddon(attachAddon);
        terminal.open(terminalContainer);
        terminal.focus();
    }

• not working

This is a floating error, because sometimes autoscroll to buttom is work, but often is not work.

[Tyriar]

Are there any errors in the devtools console?

[DmG-tech]

No errors, only this message:

[Tyriar]

I haven't seen anything like this, can you try reproduce it in the demo? https://github.com/xtermjs/xterm.js/wiki/Contributing#running-the-demo

[jerch]

@DmG-tech

Several things from my side:

• If correctly initialized, the terminal will do scroll-down automatically. Those terminal.scrollLines should not be needed.
• If your server sends byte data, terminal.write(data.data); will not work. You'd need to create an byte array first, e.g. terminal.write(new Unint8Array(data.data));. The amount of NULs in the console.log suggest, that you try something weird here. (Note that only UTF-8 is supported for byte data.)
• Have you resolved Destructive console output after exiting vim editor #4127 yet? Because if there is a fundamental misconception in your server setup, things will not work in the frontend either.

[illiav-j]

I'm having a similar problem. When I do a reset and then write multiple lines at once, there's a 50/50 chance it will be scrolled to the bottom.
I was able to reproduce it in the demo: illiav-j#1 (tested in Firefox and Chromium)

[jerch]

The term.reset() is a bit dangerous - it is a synchronous call, which disposes and re-creates half of the terminal's render chain. By the time you issue term.write the re-initialization might not be fully ready, so you run into false scroll offset calculation. term.reset is furthermore tricky, as it is not band synchronous to incoming parser data - thus should be used with great caution.

What helps here - either give term.reset some time to settle (e.g. term.reset(); setTimeout(() => term.write(next_data), 50);, or use a band synchronous VT function like RIS (e.g. term.write('\x1bc'); term.write(next_data);).

[jerch]

@Tyriar Not sure yet, if that behavior of Terminal.reset() is a recent regression (I remember having issues with it since v3.x). It seems after calling reset the terminal needs to go through at least one render cycle to get the offset calc right again (can mitigate the issue reliable by waiting ~20ms before writing new data). This prolly has to do with the viewport/scroll logic being bound to requestAnimationFrame.

Edit: Created #4603.

[illiav-j]

Thanks a lot @jerch! term.write('\x1bc'); has solved the problem for me.

[illiav-j]

It seems Terminal.clear() also exhibits similar behaviour, which explains the problem OP had.