FAQ

Why are imports being elided in my emit?

Why are function parameters are bivariant?

Why are functions with fewer parameters assignable to functions that take more parameters?

Why are functions returning non-void assignable to function returning void?

Why are all types are assignable to empty interfaces?

Why is A<string> assignable to A<number> for interface A<T> { }?

Why aren't classes nominal?

Why are enums nominal?

Why does this get orphaned on my instance methods?

Why is my output file empty when I use module exports with --outFile?

Decorators on function declarations

Why are getters without setters not considered read-only?

See Issue #12

I wrote declare var MyComponent: React.Component;, why can't I write <MyComponent />

Why don't namespaces merge across different module files?

What's the difference between enum and const enums?

What's the difference between declare class and inteface?

Can I make a type alias nominal?

How do I prevent two types from being structurally compatible?

What does it mean for an interface to extend a class?

Why am I getting an error about a missing index signature?

Why can't I use x in function f({ x: number }) { /* ... */ }?

Why don't I get type checking for (number) => string?

How do I check at runtime if an object implements some interface?

Why doesn't this incorrect cast throw a runtime error?

How do I write unit tests with TypeScript?

Why am I getting "TypeError: Cannot read property 'prototype' of undefined" in __extends ?

(Derived class put before base class)

Why do my derived class property initializers overwrite values set in the base class constructor?

See #1617 for this and other initialization order questions