console.log running before function execution completes in node.js

Question

Expected outcome: Populated array

Actual outcome: Empty array

const fs = require('fs');
const logFolder = 'app/logs/';

var timestamps = [];

fs.readdir(logFolder, (err, files) => {
    for (let file of files) {
        let timestamp = parseInt(file.slice(17, -4));
        timestamps.push(timestamp);
    }
});

console.log(timestamps);