从这里使用：
function insertAtCaret(areaId, text) {
var txtarea = document.getElementById(areaId);
if (!txtarea) {
return;
}
var scrollPos = txtarea.scrollTop;
var strPos = 0;
var br = ((txtarea.selectionStart || txtarea.selectionStart == '0') ?
"ff" : (document.selection ? "ie" : false));
if (br == "ie") {
txtarea.focus();
var range = document.selection.createRange();
range.moveStart('character', -txtarea.value.length);
strPos = range.text.length;
} else if (br == "ff") {
strPos = txtarea.selectionStart;
}
var front = (txtarea.value).substring(0, strPos);
var back = (txtarea.value).substring(strPos, txtarea.value.length);
txtarea.value = front + text + back;
strPos = strPos + text.length;
if (br == "ie") {
txtarea.focus();
var ieRange = document.selection.createRange();
ieRange.moveStart('character', -txtarea.value.length);
ieRange.moveStart('character', strPos);
ieRange.moveEnd('character', 0);
ieRange.select();
} else if (br == "ff") {
txtarea.selectionStart = strPos;
txtarea.selectionEnd = strPos;
txtarea.focus();
}
txtarea.scrollTop = scrollPos;
}
<textarea id="textareaid"></textarea>
<a href="#" onclick="insertAtCaret('textareaid', 'text to insert');return false;">Click Here to Insert</a>
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