numberOfSentences = (elm) => (elm.textContent.match(/([.?!]\s|.$)/g) ||  ).length average = (arr) => arr.reduce((a, b) => a + b) / arr.length;
This calculates the average number of setences per paragraph in a website. Sample usage:
elms = Array.from(document.getElementsByTagName('p')) average(elms.map(elm => numberOfSentences(elm)).filter(item => item !== 0))
After analysing some blog posts and news articles I found that the average paragraph is 2 to 3 sentences long. But my favorite writing advice is to focus on providing value to readers. Use the other writing tips to maximize that value.