让光标在文本框的第一个位置出现

var txtFocus = document.getElementById("ap_CarUnit");
	var position = 0;
	var userAgent=window.navigator.userAgent.toLowerCase();	
	var isMozilla = /firefox/.test(userAgent);//火狐
	var isWwebkit = /webkit/.test(userAgent);//谷歌	
	var ismsie = /msie/.test(userAgent);//IE
	var isOpera = /opera/.test(userAgent);	
	
	if(ismsie || isMozilla){
	    //如果是ie浏览器
	    var range = txtFocus.createTextRange();
	    range.move("character", position);
	    range.select();
	}
	if(isWwebkit){
		txtFocus.setSelectionRange(position, position);
                txtFocus.focus();       
	}