Difference between 'interface' and 'declare interface'

Question

What is the difference (if any) between:

declare interface SomeInterface {     //members here } 

and:

interface SomeInterface {     //members here } 

?

Answer 1

declare keyword is usually used in type definitions to describe existing classes or variables that are defined externally in JavaScript code.

There's no difference between declare interface and interface because:

• there's no code generation for interfaces and they exist only in Typescript code so you can not declare interface that's defined in JavaScript code;
• interface in Typescript by its nature is declaration only, it has no method bodies, properties values, etc. so both declare interface and interface are syntactically equal.