gist:betteralertindex.html

<button id="myButton"> Hello World! </button>
<script>
    var button = document.getElementById("myButton") 
    function speak(){ alert("hi!") } // this is a function declaration, allowing 'speak' to be used anywhere in the code, even above this line.
    //you can also assign an "anonymous function" to a variable name, but this function can only be called below where it was assigned
    //var speak = function() { alert("hi!") }
    button.onclick = speak
</script>