JavaScript: Scroll to selection after using textarea.setSelectionRange in Chrome

A JavaScript function selects a certain word in a textarea using .setSelectionRange().

In Firefox, t开发者_运维技巧he textarea automatically scrolls down to show the selected text. In Chrome (v14), it does not. Is there a way to get Chrome to scroll the textarea down to the newly selected text?

jQuery solutions are welcome.

Here is a simple and efficient solution in pure JavaScript:

// Get the textarea
var textArea = document.getElementById('myTextArea');

// Define your selection
var selectionStart = 50;
var selectionEnd = 60;
textArea.setSelectionRange(selectionStart, selectionEnd);

// Mow let’s do some math.
// We need the number of characters in a row
var charsPerRow = textArea.cols;

// We need to know at which row our selection starts
var selectionRow = (selectionStart - (selectionStart % charsPerRow)) / charsPerRow;

// We need to scroll to this row but scrolls are in pixels,
// so we need to know a row's height, in pixels
var lineHeight = textArea.clientHeight / textArea.rows;

// Scroll!!
textArea.scrollTop = lineHeight * selectionRow;

Put this in a function, extend the prototype of JavaScript's Element object with it, and you're good.

A lot of answers, but the accepted one doesn't consider line breaks, Matthew Flaschen didn't add the solution code, and naXa answer has a mistake. The simplest solution code is:

textArea.focus();

const fullText = textArea.value;
textArea.value = fullText.substring(0, selectionEnd);
textArea.scrollTop = textArea.scrollHeight;
textArea.value = fullText;

textArea.setSelectionRange(selectionStart, selectionEnd);

You can see how we solved the problem in ProveIt (see highlightLengthAtIndex). Basically, the trick is to truncate the textarea, scroll to the end, then restore the second part of the text. We also used the textSelection plugin for consistent cross-browser behavior.

Valeriy Katkov's elegant solution works great but has two problems:

1. It does not work for long strings
2. Selected contents are scrolled to the bottom of the textarea, making it hard to see the context which surrounds the selection

Here's my improved version that works for long strings (tested with at least 50,000 words) and scroll selection to the center of the textarea:

function setSelectionRange(textarea, selectionStart, selectionEnd) {
    // First scroll selection region to view
    const fullText = textarea.value;
    textarea.value = fullText.substring(0, selectionEnd);
    // For some unknown reason, you must store the scollHeight to a variable
    // before setting the textarea value. Otherwise it won't work for long strings
    const scrollHeight = textarea.scrollHeight
    textarea.value = fullText;
    let scrollTop = scrollHeight;
    const textareaHeight = textarea.clientHeight;
    if (scrollTop > textareaHeight){
        // scroll selection to center of textarea
        scrollTop -= textareaHeight / 2;
    } else{
        scrollTop = 0;
    }
    textarea.scrollTop = scrollTop;

    // Continue to set selection range
    textarea.setSelectionRange(selectionStart, selectionEnd);
}

It works in Chrome 72, Firefox 65, Opera 58, and Edge 42.

For an example of using this function, see my GitHub project SmartTextarea.

This is a code inspired by the Matthew Flaschen's answer.

/**
 * Scroll textarea to position.
 *
 * @param {HTMLInputElement} textarea
 * @param {Number} position
 */
function scrollTo(textarea, position) {
    if (!textarea) { return; }
    if (position < 0) { return; }

    var body = textarea.value;
    if (body) {
        textarea.value = body.substring(0, position);
        textarea.scrollTop = position;
        textarea.value = body;
    }
}

Basically, the trick is to truncate the textarea, scroll to the end, then restore the second part of the text.

Use it as follows

var textarea, start, end;
/* ... */

scrollTo(textarea, end);
textarea.focus();
textarea.setSelectionRange(start, end);

Based on the idea from naXa and Valeriy Katkov, I refined the function with fewer bugs. It should work out of the box (It's written with TypeScript. For JavaScript, just remove the type declaration):

function scrollTo(textarea: HTMLTextAreaElement, offset: number) {
    const txt = textarea.value;
    if (offset >= txt.length || offset < 0)
      return;

    // Important, so that scrollHeight will be adjusted
    textarea.scrollTop = 0;

    textarea.value = txt.substring(0, offset);
    const height = textarea.scrollHeight;
    textarea.value = txt;

    // Margin between selection and top of viewport
    textarea.scrollTop = height - 40;
}

Usage:

let textarea, start, end;
/* ... */

scrollTo(textarea, start);
textarea.focus();
textarea.setSelectionRange(start, end);

Complete code for Chrome:

<script type="text/javascript">
    var SAR = {};

    SAR.find = function () {
        debugger;
        var parola_cercata = $("#text_box_1").val(); // The searched word

        // Make text lowercase if search is
        // supposed to be case insensitive
        var txt = $('#remarks').val().toLowerCase();
        parola_cercata = parola_cercata.toLowerCase();

        // Take the position of the word in the text
        var posi = jQuery('#remarks').getCursorPosEnd();

        var termPos = txt.indexOf(parola_cercata, posi);

        if (termPos !== -1) {
            debugger;
            var target = document.getElementById("remarks");
            var parola_cercata2 = $("#text_box_1").val();

            // Select the textarea and the word
            if (target.setSelectionRange) {

                if ('selectionStart' in target) {
                    target.selectionStart = termPos;
                    target.selectionEnd = termPos;
                    this.selectionStart = this.selectionEnd = target.value.indexOf(parola_cercata2);
                    target.blur();
                    target.focus();
                    target.setSelectionRange(termPos, termPos + parola_cercata.length);
                }
            } else {
                var r = target.createTextRange();
                r.collapse(true);
                r.moveEnd('character', termPos + parola_cercata);
                r.moveStart('character', termPos);
                r.select();
            }
        } else {
            // Not found from cursor pos, so start from beginning
            termPos = txt.indexOf(parola_cercata);
            if (termPos !== -1) {
                var target = document.getElementById("remarks");
                var parola_cercata2 = $("#text_box_1").val();

                // Select the textarea and the word
                if (target.setSelectionRange) {

                    if ('selectionStart' in target) {
                        target.selectionStart = termPos;
                        target.selectionEnd = termPos;
                        this.selectionStart = this.selectionEnd = target.value.indexOf(parola_cercata2);
                        target.blur();
                        target.focus();
                        target.setSelectionRange(termPos, termPos + parola_cercata.length);
                    }
                } else {
                    var r = target.createTextRange();
                    r.collapse(true);
                    r.moveEnd('character', termPos + parola_cercata);
                    r.moveStart('character', termPos);
                    r.select();
                }
            } else {
                alert("not found");
            }
        }
    };


    $.fn.getCursorPosEnd = function () {
        var pos = 0;
        var input = this.get(0);
        // IE support
        if (document.selection) {
            input.focus();
            var sel = document.selection.createRange();
            pos = sel.text.length;
        }
        // Firefox support
        else if (input.selectionStart || input.selectionStart === '0')
            pos = input.selectionEnd;
        return pos;
    };
</script>

I published an answer here:

http://blog.blupixelit.eu/scroll-textarea-to-selected-word-using-javascript-jquery/

It works perfectly with just one needed rule: Set a line-height in the CSS content of the textarea!

It calculate the position of the word to scroll to just by doing some simple mathematical calculation and it worked perfectly in all my experiments!