Quick notes

• GET /posts looks good
• GET /posts/:postId looks good as well. You could maybe use Array.find (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/find) to make it easier to retrieve the post in the array.

For the DELETE route, you tried using the delete keyword. However, as written, this will delete the variable found (setting its value to undefined in the process), but it will not affect the array. To modify the array in place, you could use the Array.splice method (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/splice). Alternatively, you could create a new array without the deleted post, and change the value of the posts variable. In that case, you will probably have the change the const posts = ... line to let posts = ... if you want to be able to re-assign a value to posts.