js.js

// generate list of values from list of objects's values for a key
var colors = events.map(function(a) {return a.color;});

// add onload, instead of replace
window.addEventListener("load", function_reference);

// Async Request
var xhr = new XMLHttpRequest();
xhr.open("POST", destination_path, true);
xhr.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
xhr.onload = function(){
    console.log(this.responseText);
};
xhr.send('arg1='+val1+'&arg2='+val2);