Looks pretty good. Here's my feedback

• GET /posts: nothing to say, works as expected :).
• GET /posts/:postId: good use of the Array.find method. For the return value in the res.send method, you should use the post itself (as a JavaScript object) instead of sending an HTML string. REST API normally just send the raw data as JavaScript objects (in JSON). The raw data is then formatted in HTML properly on the client-side (in the next module, you will see how to do this using React).
• GET /posts/:postId/delete : the goal of this route is to remove a post from the array. You should take a look at the array methods which would help you do this: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array.