点击标签，将标签内容插入到textarea文档中。

function insertAtCursor(myField, myValue) {

if (document.selection) {

myField.focus();

sel = document.selection.createRange();

sel.text = myValue;

sel.select();

} else if (myField.selectionStart || myField.selectionStart == '0') {

var startPos = myField.selectionStart;

var endPos = myField.selectionEnd;

var beforeValue = myField.value.substring(0, startPos);

var afterValue = myField.value.substring(endPos, myField.value.length);

myField.value = beforeValue + myValue + afterValue;

myField.selectionStart = startPos + myValue.length;

myField.selectionEnd = startPos + myValue.length;

myField.focus();

} else {

myField.value += myValue;

myField.focus();

}

}

insertAtCursor(textarea, tag);//第一个参数是textarea，第二个参数是需要插入的tag内容