globalThis is the future.
First, TypeScript files have two kinds of scopes
global scope
If your file hasn’t any import
or export
line, this file would be executed in global scope that all declaration in it are visible outside this file.
So we would create global variables like this:
// xx.d.ts
declare var age: number
// or
// xx.ts
// with or without declare keyword
var age: number
// other.ts
globalThis.age = 18 // no error
All magic come from
var
. Replacevar
withlet
orconst
won’t work.
module scope
If your file has any import
or export
line, this file would be executed within its own scope that we need to extend global by declaration-merging.
// xx[.d].ts
declare global {
var age: number;
}
// other.ts
globalThis.age = 18 // no error
You can see more about module in official docs