This Lesson is for PRO Members.

Subscribe today and get access to all lessons! Plus direct HD download
for offline use, member comment forums, and iTunes "podcast" RSS feed.
Level up your skills now!

UNLOCK THIS LESSON

Already subscribed? Sign In

HIDE PLAYLIST

Understand lookup types in TypeScript


Lookup types, introduced in TypeScript 2.1, allow us to dynamically create types based on the property keys of an object. We'll use the function spyOn from Jest to illustrate how lookup types can type-safe function parameters.