Any and Unknown

The types any and unknown are used when we don't know the type of a value (e.g. dynamic content like parsed json).

Any

The type any essentially disables type-checking for a value. A variable with type any can be assigned any value, passed to any function, and called with any arguments, etc.

Unknown

The type unknown is the type-safe version of any. A variable with type unknown can't be used for anything without first refining it to another type.

Many standard library functions use any, but we should generally use unknown instead. Unknown is relatively new - otherwise more standard library functions would probably use it.

Checking unknown keys

Due to current limitations of the in operator, it's difficult to check if a key exists on an unknown value.

This is one case where any may make more sense for convenience. However, you can define a type guard function to accomplish this.

We'll cover type guards in more detail right after this