Question

$.post("http://openexchangerates.org/", parameters,
    function (data) {
        var currencyData = eval('( '+data+')');
        currency = currencyData["currency"];
    }
);
// I want to access currency here. But I am unable to access it.

Answer 1

try declaring the currency variable outside the ajax function.
you can set it a default value at first to prevent ambiguity if it returns ‘undefined’ (for debug purposes)

function getCurrency(){

    var currency = 'debug'; //TODO: remove this value once code works. 

    $.post("http://openexchangerates.org/", parameters,
        function (data) {
        var currencyData = eval('( '+data+')');
        currency = currencyData["currency"];
    }
    );

    console.log(currency);

}