javascript 更新 textarea 值，但保持光标位置
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update textarea value, but keep cursor position
提问by Ben Noland
I have an html textarea that will be updated periodically via javascript.
我有一个 html textarea，它将通过 javascript 定期更新。
when I do this:
当我这样做时：
$("#textarea").val(new_val);
The cursor moves to the end of the text.
光标移动到文本的末尾。
I would like to update the text without changing the cursor position. Also, if the user has a range of text selected, the highlight should be preserved.
我想在不更改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。
回答by Tim Down
Here is a pair of functions that get and set the selection/caret position in a text area in all major browsers.
这是在所有主要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。
Note: if you don't need to support IE <= 8, just use the selectionStartand selectionEndproperties (MDN). All of the complicated code below is just there to support old versions of IE.
注意：如果您不需要支持 IE <= 8，只需使用selectionStart和selectionEnd属性（MDN）。下面所有复杂的代码只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();
}
}
When you change the textarea's value, first save the selection, then restore it afterwards:
当您更改 textarea 的值时，首先保存选择，然后再恢复它：
var t = document.getElementById("textarea");
var sel = getInputSelection(t);
t.value = some_new_value;
setInputSelection(t, sel.start, sel.end);
