this.FuncName = function (variable) {
$.ajax(
                {
                    type: "POST",
                    url: '/.../...',
                    data: function(variable) {
                        if (variable) {
                JSON.stringify({ field1: value1, field2: value2 }),
            } else {
                JSON.stringify({ field1: value3, field2: value4 }),
            }
                    },
            ...
        }