{"id":11139,"library":"jest-get-type","title":"Jest Get Type Utility","description":"The `jest-get-type` package provides a core utility function, `getType`, designed to accurately determine the type of any JavaScript value (e.g., 'array', 'object', 'string', 'null', 'undefined', 'function', 'symbol'). It is an integral part of the Jest testing framework's monorepo, ensuring consistent type identification across Jest's various internal components. The current specific package version is 29.6.3, aligning with the Jest 29 ecosystem. However, the broader Jest framework recently released its major version 30.0.0, which targets more frequent major releases after a significant previous gap. This utility is primarily used internally by Jest, but can also be imported directly for robust, Jest-aligned type checking in other projects, especially when consistency with Jest's internal logic is desired. It ships with TypeScript types for an enhanced developer experience.","status":"active","version":"29.6.3","language":"javascript","source_language":"en","source_url":"https://github.com/jestjs/jest","tags":["javascript","typescript"],"install":[{"cmd":"npm install jest-get-type","lang":"bash","label":"npm"},{"cmd":"yarn add jest-get-type","lang":"bash","label":"yarn"},{"cmd":"pnpm add jest-get-type","lang":"bash","label":"pnpm"}],"dependencies":[],"imports":[{"note":"Preferred for modern projects using ESM and TypeScript. Jest 30 generally pushes towards ESM.","wrong":"const getType = require('jest-get-type');","symbol":"getType","correct":"import { getType } from 'jest-get-type';"},{"note":"For CommonJS environments. This package uses named exports.","wrong":"import getType from 'jest-get-type';","symbol":"getType","correct":"const { getType } = require('jest-get-type');"},{"note":"Importing the TypeScript type definition for `getType`'s return values or signature.","wrong":"import { GetType } from 'jest-get-type';","symbol":"GetType","correct":"import type { GetType } from 'jest-get-type';"}],"quickstart":{"code":"import { getType } from 'jest-get-type';\n\nconsole.log(getType(1)); // Outputs: 'number'\nconsole.log(getType('hello')); // Outputs: 'string'\nconsole.log(getType(true)); // Outputs: 'boolean'\nconsole.log(getType({})); // Outputs: 'object'\nconsole.log(getType([])); // Outputs: 'array'\nconsole.log(getType(null)); // Outputs: 'null'\nconsole.log(getType(undefined)); // Outputs: 'undefined'\nconsole.log(getType(() => {})); // Outputs: 'function'\nconsole.log(getType(Symbol('foo'))); // Outputs: 'symbol'\n\ninterface MyObject {\n  a: number;\n  b: string;\n}\n\nconst obj: MyObject = { a: 1, b: 'test' };\nconsole.log(getType(obj)); // Outputs: 'object'","lang":"typescript","description":"Demonstrates importing `getType` and using it to determine the type of various JavaScript primitives and objects."},"warnings":[{"fix":"Ensure your development and CI/CD environments are running Node.js 18.x or a more recent LTS version before upgrading Jest.","message":"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.","severity":"breaking","affected_versions":">=30.0.0"},{"fix":"Update your TypeScript dependency to `typescript@^5.4.0` or a newer compatible version.","message":"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.","severity":"breaking","affected_versions":">=30.0.0"},{"fix":"After upgrading Jest, run tests with the `-u` flag (`jest -u`) to update all snapshots. Review changes carefully.","message":"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.","severity":"gotcha","affected_versions":">=30.0.0"},{"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.","message":"`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.","severity":"gotcha","affected_versions":">=29.0.0"}],"env_vars":null,"last_verified":"2026-04-19T00:00:00.000Z","next_check":"2026-07-18T00:00:00.000Z","problems":[{"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.","cause":"Incorrect import statement when mixing CommonJS and ESM modules, or trying to default import a named export.","error":"TypeError: (0, jest_get_type_1.getType) is not a function"},{"fix":"Upgrade your Node.js environment to version 18.x or higher. Check your project's `.nvmrc` or CI/CD configuration.","cause":"Running a project with Jest 30 (or `jest-get-type` v30+) on an unsupported Node.js version.","error":"Jest requires Node.js 18 or newer."},{"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`).","cause":"Missing `@types/jest` or `jest-get-type` package, or incorrect TypeScript configuration.","error":"TS2307: Cannot find module 'jest-get-type' or its corresponding type declarations."}],"ecosystem":"npm"}