更新 textarea 值，但保持光标位置

Question

我有一个 html 文本区域，它将通过 javascript 定期更新。

当我这样做时：

$("#textarea").val(new_val);

光标移动到文本末尾。

我想在不改变光标位置的情况下更新文本。此外，如果用户选择了一系列文本，则应保留突出显示。

Answer 1

这是在所有主流浏览器的文本区域中获取和设置选择/插入符号位置的一对函数。

注意：如果您不需要支持 IE selectionStart 和 selectionEnd 属性 (MDN)。下面所有复杂的代码都是为了支持旧版本的 IE。

function getInputSelection(el) {
    var start = 0, end = 0, normalizedValue, range,
        textInputRange, len, endRange;

    if (typeof el.selectionStart == "number" && typeof el.selectionEnd == "number") {
        start = el.selectionStart;
        end = el.selectionEnd;
    } else {
        range = document.selection.createRange();

        if (range && range.parentElement() == el) {
            len = el.value.length;
            normalizedValue = el.value.replace(/\r\n/g, "\n");

            // Create a working TextRange that lives only in the input
            textInputRange = el.createTextRange();
            textInputRange.moveToBookmark(range.getBookmark());

            // Check if the start and end of the selection are at the very end
            // of the input, since moveStart/moveEnd doesn't return what we want
            // in those cases
            endRange = el.createTextRange();
            endRange.collapse(false);

            if (textInputRange.compareEndPoints("StartToEnd", endRange) > -1) {
                start = end = len;
            } else {
                start = -textInputRange.moveStart("character", -len);
                start += normalizedValue.slice(0, start).split("\n").length - 1;

                if (textInputRange.compareEndPoints("EndToEnd", endRange) > -1) {
                    end = len;
                } else {
                    end = -textInputRange.moveEnd("character", -len);
                    end += normalizedValue.slice(0, end).split("\n").length - 1;
                }
            }
        }
    }

    return {
        start: start,
        end: end
    };
}

function offsetToRangeCharacterMove(el, offset) {
    return offset - (el.value.slice(0, offset).split("\r\n").length - 1);
}

function setInputSelection(el, startOffset, endOffset) {
    if (typeof el.selectionStart == "number" && typeof el.selectionEnd == "number") {
        el.selectionStart = startOffset;
        el.selectionEnd = endOffset;
    } else {
        var range = el.createTextRange();
        var startCharMove = offsetToRangeCharacterMove(el, startOffset);
        range.collapse(true);
        if (startOffset == endOffset) {
            range.move("character", startCharMove);
        } else {
            range.moveEnd("character", offsetToRangeCharacterMove(el, endOffset));
            range.moveStart("character", startCharMove);
        }
        range.select();
    }
}

当你改变textarea的值时，先保存选择，然后再恢复：

var t = document.getElementById("textarea");
var sel = getInputSelection(t);
t.value = some_new_value;
setInputSelection(t, sel.start, sel.end);

Answer 2

十年后，但这就是我想出的用于替换文本区域中的项目的方法。当替换为更长或更短的文本时，需要一些额外的处理来调整插入符号或选择。

// find and replace in textarea while preserving caret and selection
function replaceText(el, findText, replaceWithText) {
    var text = el.value;
    var selectionStart = 0;
    var selectionEnd = 0;
  // only support modern browsers for preserving caret and selection
    if (el.setSelectionRange) {
        selectionStart = el.selectionStart;
        selectionEnd = el.selectionEnd;
    }
    var start = 0;
    while ((start = text.indexOf(findText, start)) > -1) {
        var end = start + findText.length;
        text = text.substr(0, start) + replaceWithText + text.substr(end);
        if (selectionStart < end) {
            selectionStart = Math.min(selectionStart, start + replaceWithText.length);
        } else {
            selectionStart = selectionStart + replaceWithText.length - (end - start);
        }
        if (selectionEnd < end) {
            selectionEnd = Math.min(selectionEnd, start + replaceWithText.length);
        } else {
            selectionEnd = selectionEnd + replaceWithText.length - (end - start);
        }
        start += replaceWithText.length;
    }
  // don't do anything unless we need to (otherwise destroys undo)
    if (el.value != text) { 
        el.value = text;
        if (el.setSelectionRange) {
            el.selectionStart = selectionStart;
            el.selectionEnd = selectionEnd;
        }
    }
}

Place caret on or after the word LONGER, or select some text after or including it:
<br />
<textarea id='t'>Here is
some LONGERtext
to replace</textarea>
<br />
<input type="button" onclick="replaceText(document.getElementById('t'),'LONGER',''); document.getElementById('t').focus();" value="remove word LONGER" />