javascript 验证身份证号码

<script type="text/javascript">
	// 去左右空格 
	function trim(str){
		return str.replace(/^\s+|\s+$/g,'');
	}

	var powers=new Array("7","9","10","5","8","4","2","1","6","3","7","9","10","5","8","4","2");      
    var parityBit=new Array("1","0","X","9","8","7","6","5","4","3","2");      
    var sex="male";      
    //校验身份证号码的主调用
    function validId(obj){      
        var _id=obj.value;      
        if(trim(_id)==""){
        	obj.value="";
        	document.getElementById("idCardMsg").innerHTML = "请输入身份证号。";
      		return false;
        } 
        if(_id.length.length != 15 && _id.length != 18){
        	document.getElementById("idCardMsg").innerHTML = "请输入15位或者18位身份证号码。";
      		return false;
        }
        var _valid=false;      
        if(_id.length==15){      
            _valid=validId15(_id);      
        }else if(_id.length==18){      
            _valid=validId18(_id);      
        }      
        if(!_valid){      
            document.getElementById("idCardMsg").innerHTML = "身份证号码有误,请检查!";
            obj.focus();      
            return false;      
        }
        document.getElementById("idCardMsg").innerHTML = "输入正确。";
        return true;
    }          
    //校验18位的身份证号码      
     
    function validId18(_id){      
        _id=_id+"";      
        var _num=_id.substr(0,17);      
        var _parityBit=_id.substr(17);      
        var _power=0;      
        for(var i=0;i< 17;i++){      
            //校验每一位的合法性     
            if(_num.charAt(i)<'0'||_num.charAt(i)>'9'){      
                return false;      
                break;      
            }else{      
                //加权 
				_power+=parseInt(_num.charAt(i))*parseInt(powers[i]);          
            }      
        }      
	    //取模      
        var mod=parseInt(_power)%11;
		if(parityBit[mod]==_parityBit){      
            return true;      
        }      
        return false;      
    }      
    //校验15位的身份证号码      
     
    function validId15(_id){      
        _id=_id+"";      
        for(var i=0;i<_id.length;i++){      
            //校验每一位的合法性      
     
            if(_id.charAt(i)<'0'||_id.charAt(i)>'9'){      
                return false;      
                break;      
            }      
        }      
        var year=_id.substr(6,2);      
        var month=_id.substr(8,2);      
        var day=_id.substr(10,2);      
        var sexBit=_id.substr(14);      
        //校验年份位      
     
        if(year<'01'||year >'90')return false;      
        //校验月份      
     
        if(month<'01'||month >'12')return false;      
        //校验日      
     
        if(day<'01'||day >'31')return false;         
        return true;      
    }  
</script>

<input type="text" onblur="javascript:validId(this)"  maxlength="20"/>
<span id="idCardMsg"></span>