Errors & Validation
The problem we should have encountered in the last step is that Express was treating our numeric path parameters as strings!
Instead of doing 1 + 2 and getting the number 3, we are doing '1' + '2' and getting the string '12'.
This is because Express automatically treats all route parameters (and query string parameters) as strings. You should have worked out by this point (either on your own or with the solution) that we need to transform these strings to numbers before we use them in our controllers.
What if the user doesn't pass through a valid number though? Say they pass in fish and chips. Try it in Postman. Visit http://localhost:3000/numbers/add/fish/and/chips. You should get back a response of:
This is because when we do parseInt on fish or chips we get back NaN, so we're trying to do NaN + NaN, which isn't a valid response. We should instead be validating that our numbers are valid, and if not then we should be responding with a status code that is typically linked to an error e.g. 400 Bad Request or 404 Not Found.
- Read about HTTP status codes on MDN
Challenge
Check that your numbers are both valid (hint: see Number.isNaN). If one or both are invalid, then respond to the user with a 400 status code. Be sure to check in Postman that it does return a 400.
Extra credit
Write a test that passes in fish and chips, and assert that a 400 is returned.
Solution
- Find the solution to the above challenge here.