var a='account.type=1&account.id=&account.dependFlag=0&account.card.companyId=1&account.name=%E4%B8%AD%E9%93%B6VISA%E5%8D%A1&account.hidden=&account.card.cardNo=&account.moneyTypeId=0&account.card.billDay=1&account.card.repayType=0&account.card.repayDay=20&account.card.alert=2&account.comment=%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D';

var root={};

a.split('&').sort().map(function(s){

    var p=root;

    s.match(/(.+?)(?:\.|=)/g).map(function(ss){

        var t=ss.slice(0,-1);

        p[t]=p[t]||((ss.slice(-1)==='=')?decodeURIComponent(s.match(/=(.*)$/)[1]):{});

        p=p[t];

    });

});

console.log(root);