Mixpanel .track() with no dependencies

vanillaTrackStuff.js

//a vanilla implementation of .track()
//docs: https://developer.mixpanel.com/docs/http 
//by AK

function trackStuff(uuid, eventName, props, token) {
    //the mixpanel data model
    let spec = {
        "event": eventName,
        "properties": {
            // these two properties are required!
            "distinct_id": uuid,
            "token": token
        }
    };

    //iterate through props
    if (props) {
        for (prop in props) {
            //append them to our spec
            spec.properties[prop] = props[prop];
        }
    }

    // base64 encode
    let payload = btoa(JSON.stringify(spec));

    //make a vanilla HTTP request as per: https://developer.mixpanel.com/docs/http#section-tracking-events
    let xhttp = new XMLHttpRequest();
    xhttp.onreadystatechange = function() {
        if (this.readyState === 4 && this.status === 200) {
            console.log("data sent");
        }
    };
    xhttp.open("GET", "https://api.mixpanel.com/track/?data=" + payload + "&ip=1", true);
    xhttp.send();
}

// how we might use this
let someProps = {
    "user type": "maverick",
    "interests": ["foo", "bar", "baz", "qux"]
};
trackStuff("ak!", "App Open", someProps, "009c696fd3f040f5b32297ac50845210");