java script code unfamiliar syntax making confusion

Following code is from Facebook login page. I have been trying to understand it for some time but it's just not making any sense. Can any please explain line by line what is code and something about the syntax.

Lines like window.requireLazy(['Env'],b); I have no idea what it is about

function envFlush(a) {
    function b(c) {
        for (var d in a) c[d] = a[d];
    }
    if (window.requireLazy) {
        window.requireLazy(['Env'], b);
    } else {
        window.Env = window.Env || {};
        b(window.Env);
    }
}
envFlush({
    "ajaxpipe_token": "AXg5CspRWrtm_Ip3",
    "lhsh": "qAQFhKTYS",
    "khsh": "0`sj`e`rm`s-0fdu^gshdoer-0gc^eurf-3gc^eurf;1;enbtldou;fduDmdldourCxO`ld-2YLMIuuqSdptdru;qsnunuxqd;rdoe"
});

Any help will be appreciated also from where the function envFlush get called?