Ranking algo for social media feed

ranker.js

// So this is the model I have now (in JavaScript):


var GRACE_PERIOD_MILLIS =  259200000; // 3 days worth of milliseconds

function getRanking(post) {

    var millis = post.dateCreated.getTime(); //get milliseconds since post was first posted
    var currentMillis = Date.now();   //get current milliseconds since epoch
    var diff1 = ((millis + GRACE_PERIOD_MILLIS) / currentMillis) - 1;
    var diff2 = currentMillis- millis;

    return (diff1) / (post.upvotes.length + 1) + (post.upvotes.length + 1) / (diff2);
}

// but we could do this instead using Math.log:

function getRanking(post) {

    var millis = post.dateCreated.getTime(); //get milliseconds since post was first posted
    var currentMillis = Date.now();   //get current milliseconds since epoch
    var diff1 = ((millis + GRACE_PERIOD_MILLIS) / currentMillis) - 1;
    var diff2 = currentMillis- millis;

    return (diff1) / (post.upvotes.length + 1) + Math.log(post.upvotes.length + 1) / (diff2); //use the natural log for weight
}