Load and execute javascript code SYNCHRONOUSLY

If you use this:

function loadScriptSync (src) {
    var s = document.createElement('script');
    s.src = src;
    s.type = "text/javascript";
    s.async = false;                                 // <-- this is important
    document.getElementsByTagName('head')[0].appendChild(s);
}

You can do what you want (although divided up in an additional script file)

test.html (code inside a script tag):

loadScriptSync("script.js");
loadScriptSync("sayhi.js"); // you have to put the invocation into another script file

script.js:

function SayHi() {
     console.log("hi");
}

sayhi.js:

SayHi();