光标操作

// 获取光标位置
function getCursorPosition(dom) {
    var cursorPos = 0;   
    if (document.selection) {
    	// IE Support
        dom.focus();
        var range = document.selection.createRange();
        range.moveStart ('character', -dom.value.length);
        cursorPos = range.text.length;
    } else if (dom.selectionStart || dom.selectionStart == '0'){
    	// Firefox support
    	cursorPos = dom.selectionStart;
    }
        
    return cursorPos;
}

// 设置光标位置
function setCursorPosition(dom, pos){
    if(dom.setSelectionRange) {
        dom.focus();
        dom.setSelectionRange(pos, pos);
    }
    else if (dom.createTextRange) {
        var range = dom.createTextRange();
        range.collapse(true);
        range.moveEnd('character', pos);
        range.moveStart('character', pos);
        range.select();
    }
}