Rest service Parameters

I need to construct and concatenate a dynamic parameter string for a json restservice if I have one value in the parameter it looks like:
var A = localStorage.getItem('account');
return '{"account":"' + A + '"}'
This works and produces the value:      {"account":"systems"}
I need to pass another parameter in the same string but am struggling with how to achieve this, the string should end up looking like:
{"account":"systems" , “password”:”abc123”}
I have
var A = localStorage.getItem('account');
var P = localStorage.getItem('password');

What is the correct syntax to construct the string?