Jest: TypeError: Cannot read property of undefined

Question

Im trying to test my React class, that has import dotnetify from "dotnetify"; import. That works fine, but Jest says, that dotnetify is undefined. If i change to const dotnetify = require("dotnetify"); , Jest passes test, but this is silly workaround. How to explain Jest, that dotnetify is not undefined?

Than you in advance.

Answer 1

This cannot be 'explained' to Jest, it's really undefined.

There are several ways to handle CommonJS modules in TypeScript. As explained in this answer , there will be default import in CommonJS packge only if synthetic imports were enabled with esModuleInterop ( allowSyntheticDefaultImports ) compiler option.

Otherwise it should be done like:

import * as dotnetify from "dotnetify";

Or with TypeScript-specific syntax:

import dotnetify = require("dotnetify")