Jest Get Type Utility

Common errors

• TypeError: (0, jest_get_type_1.getType) is not a function

  cause Incorrect import statement when mixing CommonJS and ESM modules, or trying to default import a named export.
  fix If using CommonJS, ensure `const { getType } = require('jest-get-type');`. If using ESM, ensure `import { getType } from 'jest-get-type';`. Do not use `import getType from 'jest-get-type';` as it is not a default export.

• Jest requires Node.js 18 or newer.

  cause Running a project with Jest 30 (or `jest-get-type` v30+) on an unsupported Node.js version.
  fix Upgrade your Node.js environment to version 18.x or higher. Check your project's `.nvmrc` or CI/CD configuration.

• TS2307: Cannot find module 'jest-get-type' or its corresponding type declarations.

  cause Missing `@types/jest` or `jest-get-type` package, or incorrect TypeScript configuration.
  fix Ensure `jest-get-type` and `@types/jest` (if Jest is also installed) are in your `devDependencies`. Verify `tsconfig.json` includes `node_modules/@types` in `typeRoots` and `moduleResolution` is set appropriately (e.g., `bundler`, `node16`, or `nodenext`).

Warnings

• breaking When upgrading to Jest 30 (which includes upgrading Jest's sub-packages like `jest-get-type` to v30+), Node.js versions 14, 16, 19, and 21 are no longer supported. Projects must use Node.js 18.x or newer.
  Fix: Ensure your development and CI/CD environments are running Node.js 18.x or a more recent LTS version before upgrading Jest.
• breaking Projects upgrading to Jest 30 (and thus `jest-get-type` v30+) must also update their TypeScript version to 5.4 or newer. Using older TypeScript versions with Jest 30 types will result in compilation errors.
  Fix: Update your TypeScript dependency to `typescript@^5.4.0` or a newer compatible version.
• gotcha Upgrading to Jest 30 may necessitate regenerating all snapshots due to changes in snapshot header formats and the removal of deprecated `goo.gl` links. While not directly related to `jest-get-type`'s API, it is a common side effect for any project migrating their Jest setup.
  Fix: After upgrading Jest, run tests with the `-u` flag (`jest -u`) to update all snapshots. Review changes carefully.
• gotcha `jest-get-type` is primarily an internal utility of the Jest monorepo. While exported, its API and development are driven by Jest's core needs, which may lead to less independent feature development or versioning compared to standalone libraries.
  Fix: Be aware that direct external dependencies on internal Jest utilities like `jest-get-type` might be subject to changes aligned with Jest's overall architecture rather than external consumer needs. Always check Jest's main changelog for broader context.

Install

• npm install jest-get-type npm
• yarn add jest-get-type yarn
• pnpm add jest-get-type pnpm

Imports

• getType
  wrong:

  const getType = require('jest-get-type');

  correct:

  import { getType } from 'jest-get-type';

  Preferred for modern projects using ESM and TypeScript. Jest 30 generally pushes towards ESM.
• getType
  wrong:

  import getType from 'jest-get-type';

  correct:

  const { getType } = require('jest-get-type');

  For CommonJS environments. This package uses named exports.
• GetType
  wrong:

  import { GetType } from 'jest-get-type';

  correct:

  import type { GetType } from 'jest-get-type';

  Importing the TypeScript type definition for `getType`'s return values or signature.

Quickstart

Demonstrates importing `getType` and using it to determine the type of various JavaScript primitives and objects.

import { getType } from 'jest-get-type';

console.log(getType(1)); // Outputs: 'number'
console.log(getType('hello')); // Outputs: 'string'
console.log(getType(true)); // Outputs: 'boolean'
console.log(getType({})); // Outputs: 'object'
console.log(getType([])); // Outputs: 'array'
console.log(getType(null)); // Outputs: 'null'
console.log(getType(undefined)); // Outputs: 'undefined'
console.log(getType(() => {})); // Outputs: 'function'
console.log(getType(Symbol('foo'))); // Outputs: 'symbol'

interface MyObject {
  a: number;
  b: string;
}

const obj: MyObject = { a: 1, b: 'test' };
console.log(getType(obj)); // Outputs: 'object'