What does the "as" keyword do?

Question

if (process.env.NODE_ENV !== 'production') {     (WithUser as any).displayName = wrapDisplayName(Component, 'withUser'); } 

I'm not even sure if as is a keyword, but anyway, what does it do in JavaScript?

Answer 1

That is not vanilla JavaScript, it is TypeScript. As any means consider the typed object as a plain untyped JavaScrpt object.

The as keyword is a Type Assertion in TypeScript which tells the compiler to consider the object as another type than the type the compiler infers the object to be.

Answer 2

It's TypeScript, not vanilla JS, but for the as itself: It's called Type Assertion, you are just telling the compiler to treat something as a type:

var a = 'TEST STRING' var b = a as string; //Means the compiler will assume it's a string 

It's equivalent to this:

var a = 'TEST STRING' var b = <string> a;  

However it might be confusing when working with JSX (JS with html tags) , so in those cases the as syntax is preferred.