ethicalhack3r ethicalhack3r - 1 year ago 63
Javascript Question

Find out the 'line' (row) number of the cursor in a textarea

I would like to find out and keep track of the 'line number' (rows) of the cursor in a textarea. (The 'bigger picture' is to parse the text on the line every time a new line is created/modified/selected, if of course the text was not pasted in. This saves parsing the whole text un-necessarily at set intervals.)

There are a couple of posts on StackOverflow however none of them specifically answer my question, most questions are for cursor position in pixels or displaying lines numbers besides the textarea.

My attempt is below, it works fine when starting at line 1 and not leaving the textarea. It fails when clicking out of the textarea and back onto it on a different line. It also fails when pasting text into it because the starting line is not 1.

My JavaScript knowledge is pretty limited.



<script type="text/javascript">

var total_lines = 1; // total lines
var current_line = 1; // current line
var old_line_count;

// main editor function
function code(e) {

// declare some needed vars
var keypress_code = e.keyCode; // key press
var editor = document.getElementById('editor'); // the editor textarea
var source_code = editor.value; // contents of the editor

// work out how many lines we have used in total
var lines = source_code.split("\n");
var total_lines = lines.length;

// do stuff on key presses
if (keypress_code == '13') { // Enter
current_line += 1;
} else if (keypress_code == '8') { // Backspace
if (old_line_count > total_lines) { current_line -= 1; }
} else if (keypress_code == '38') { // Up
if (total_lines > 1 && current_line > 1) { current_line -= 1; }
} else if (keypress_code == '40') { // Down
if (total_lines > 1 && current_line < total_lines) { current_line += 1; }
} else {
//document.getElementById('keycodes').innerHTML += keypress_code;

// for some reason chrome doesn't enter a newline char on enter
// you have to press enter and then an additional key for \n to appear
// making the total_lines counter lag.
if (total_lines < current_line) { total_lines += 1 };

// putput the data
document.getElementById('total_lines').innerHTML = "Total lines: " + total_lines;
document.getElementById('current_line').innerHTML = "Current line: " + current_line;

// save the old line count for comparison on next run
old_line_count = total_lines;





<textarea id="editor" rows="30" cols="100" value="" onkeydown="code(event)"></textarea>
<div id="total_lines"></div>
<div id="current_line"></div>



Answer Source

You would want to use selectionStart to do this.

<textarea onkeyup="getLineNumber(this, document.getElementById('lineNo'));" onmouseup="this.onkeyup();"></textarea>
<div id="lineNo"></div>


    function getLineNumber(textarea, indicator) {

        indicator.innerHTML = textarea.value.substr(0, textarea.selectionStart).split("\n").length;


This works when you change the cursor position using the mouse as well.

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