Odd side effects using eval

gistfile1.js

// run with: curl -d 'console.log("hi");' http://localhost:8063; curl -d 'console.log("hi");' http://localhost:8063
vertx.createHttpServer().requestHandler(function (req) {
    req.bodyHandler(function (buffer) {
        var code = buffer.toString("UTF-8");
        var result = eval('"use strict";' + code) || {};
        req.response().end(JSON.stringify(result));
    });
}).listen(8063);