as

In JavaScript, as is a contextual keyword that gives a binding a different name in an import or export clause. It also names the namespace object that collects all of a module’s exports in import * as and export * as statements.

In an import declaration, { original as local } creates a local binding with a new name, which avoids clashes between modules that export the same name. In an export list, { local as exported } changes the name that other modules see. Renaming to or from default reads or creates a default export.

All of these forms are module syntax that only works in a module. Outside these clauses, as isn’t reserved and stays a valid identifier, even in modules. TypeScript’s as type assertions aren’t JavaScript syntax. Renaming and import * as came with modules in ES2015, and export * as followed in ES2020. Since ES2022, modules can export string names, such as "kebab-name", and as gives them a valid local name on import.

import { <name> as <alias> } from "<specifier>";
import * as <namespace> from "<specifier>";
export { <name> as <exportedName> };
export * as <namespace> from "<specifier>";

const capitalize = (text) => text[0].toUpperCase() + text.slice(1);
const reverse = (text) => [...text].reverse().join("");

export { capitalize as title, reverse };

import { title as toTitle } from "./strings.mjs";
import * as strings from "./strings.mjs";

console.log(toTitle("ada"));
console.log(strings.reverse("stressed"));
console.log(Object.keys(strings));

$ node main.mjs
Ada
desserts
[ 'reverse', 'title' ]

> const as = "alias";
undefined
> as.toUpperCase()
'ALIAS'