Unexpected error when importing export = with function declaration

[OliverJAsh]

TypeScript Version: 3.7.3

Search Terms: import export equals = declaration types typings module function declaration expression

Code

// lib.d.ts
declare function md5(value: string, key?: string, raw?: boolean): string;

export = md5;

// Unexpected error:
// This module can only be referenced with ECMAScript imports/exports by turning on the 'esModuleInterop' flag and referencing its default export.
import * as lib from "./lib";

(Note: I have intentionally disabled allowSyntheticDefaultImports + esModuleInterop.)

Potential/known workarounds

If we use a function expression instead, the problem goes away:

// lib.d.ts
declare const md5: (value: string, key?: string, raw?: boolean) => string;

export = md5;

The problem also goes away if we add a namespace:

// lib.d.ts
declare function md5(value: string, key?: string, raw?: boolean): string;
declare namespace md5 {}

export = md5;

[RyanCavanaugh]

This is the intended behavior because import * as x can never produce a callable x per the ES spec. The other forms are allowed workarounds if you really intend to write some broken code 😉

[OliverJAsh]

Ah, thanks for clarifying that.

Given this is a valid CommonJS module definition, I'm wondering how we can import this into our TS project.

• We can't use import md5 = require('blueimp-md5') because we're targeting ES Modules
• We can't use import * as md5 from 'blueimp-md5' because ES Modules do not allow namespaces to be callable
• We can't use import md5 from 'blueimp-md5' because we haven't enabled allowSyntheticDefaultImports, nor do we want to (because it can result in runtime exceptions and we want to adhere to the ES Modules spec)

Is this case, would you recommend using one of the workarounds I mentioned above, or is there something else we should consider?

Types for blueimp-md5: https://github.com/DefinitelyTyped/DefinitelyTyped/blob/56c1ea26b59ed0e4634b1ba27096ab3b90371875/types/blueimp-md5/index.d.ts

[typescript-bot]

This issue has been marked 'Working as Intended' and has seen no recent activity. It has been automatically closed for house-keeping purposes.

[ishowta]

Why doesn't the error occur when namespace is declared? Even in that case, I think the same runtime error occur when the function is called.

[RyanCavanaugh]

Some people used downlevelers that made this incidentally work and took a hard dependency on that fact, so the namespace declaration is allowed as a workaround