将一个实体转换成 Url 参数的形式 ?a=a&b=b

function toQueryString(obj) {
var ret = [];
for (var key in obj) {
key = encodeURIComponent(key);
var values = obj[key];
if (values && values.constructor == Array) { //数组
var queryValues = [];
for (var i = 0, len = values.length, value; i < len; i++) {
value = values[i];
queryValues.push(toQueryPair(key, value));
}
ret = ret.concat(queryValues);
} else { //字符串
ret.push(toQueryPair(key, values));
}
}
return '?' + ret.join('&');
};