正則表達式取url中參數值

var url = window.location.href;
if(url.indexOf("id=") > 0) {
var id= takeParam(url, "id");
}

function takeParam(url,key){

var a = url ;
var b= key;
try {
var reg=new RegExp( b + "=[0-9a-zA-z-_]{0,}" );
return reg.exec(a).toString().split("=")[1];
} catch(e) {
console.log(e);
console.log("正則表達式取參數值錯誤" + key);
}
return "";
}