Typescript Interface Index Signature

Question

I have the following interface:

interface ClassSchedule {
  [key: string]: string;
}

However, I am receiving an error that my key is possibly undefined. How do I account for this?

interface ClassSchedule {
  [key: string]: string;
}

Answer 1

It sounds like you have the --noUncheckedIndexedAccess compiler option enabled.

You can avoid this error by:

• Disabling that compiler option (though that loses you a bit of type safety).
• Checking whether the key exists before trying to access it (e.g. by wrapping the access in an if statement).
• Adding an ! after the key (e.g. foo.bar! or `foo["bar"]!) to assert that the value will always be non-null.