nodejs readline's cursor behavior and position

Question

I have the following code

const readline = require('readline');
const {stdin, stderr} = process;
const rl = readline.createInterface({
    output: stderr,
    input: stdin
})

console.log(rl.getCursorPos());
let i = 5;
while (i > 0) {
    console.log('fill up with logs');
    i--
}
console.log(rl.getCursorPos())

and its output

{ cols: 2, rows: 0 }
fill up with logs
fill up with logs
fill up with logs
fill up with logs
{ cols: 2, rows: 0 }

as from above the last 'getCursorPos()' should return a new position since the stderr output has been filled up with logs, instead, it returns its default value, did I misunderstand the way it works?

or is there anyway I can get cursor position and save it multiple times using readline? I've looked through using asni escape, but it seems like it can only store one cursor position at a time.

DAC · Answer 1 · 2022-03-06T01:29:55.810

The position returned by readline is relative to the current cursor location, not absolute on the screen.

I was able to create a promise to get this information using the answer below containing the escape sequence for requesting terminal cursor position:

How can I get position of cursor in terminal?

const getCursorPos = () => new Promise((resolve) => {
    const termcodes = { cursorGetPosition: '\u001b[6n' };

    process.stdin.setEncoding('utf8');
    process.stdin.setRawMode(true);

    const readfx = function () {
        const buf = process.stdin.read();
        const str = JSON.stringify(buf); // "\u001b[9;1R"
        const regex = /\[(.*)/g;
        const xy = regex.exec(str)[0].replace(/\[|R"/g, '').split(';');
        const pos = { rows: xy[0], cols: xy[1] };
        process.stdin.setRawMode(false);
        resolve(pos);
    }

    process.stdin.once('readable', readfx);
    process.stdout.write(termcodes.cursorGetPosition);
})

const AppMain = async function () {
    process.stdout.write('HELLO');
    const pos = await getCursorPos();
    process.stdout.write("\n");
    console.log({ pos });
}

AppMain();

nodejs readline's cursor behavior and position

1 Answers1