Registry / http-networking / data-mocks-server

data-mocks-server

library10.0.2jsnpmunverified

Data Mocks Server is a JavaScript/TypeScript library designed for creating a standalone mock HTTP server, contrasting with client-side libraries that intercept `fetch` or `XHR` requests. It's built on Express, allowing developers to define API responses and scenarios through configuration rather than network interception. The library is currently at version 10.0.2, with its latest update in July 2024, indicating active maintenance. Releases are not on a fixed schedule but appear when features or bug fixes are available, with significant gaps between major versions like v9 to v10. Key differentiators include its server-first approach, a built-in UI for dynamic scenario switching at runtime, and comprehensive TypeScript support. It's particularly useful for end-to-end testing, local development, and showcasing features without relying on a real backend.

http-networking testing web-framework

npm install data-mocks-server

github ↗package ↗homepage ↗

INSTALL

IMPORT

SIG · DATA-MOCKS-SERVER

data-mocks-server

http-networkingjavascriptv10.0.2

Install

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Import

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Disk

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Pass rate

0/ 6

Env Coverage0 / 6

glibc

18–22

musl

18–22

Install & Compatibility

Where this runs

tested against v? · npm install

Install × environment matrix

Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux

musl

node 18–226 runs

build_error

glibc

node 18–226 runs

build_error

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

run

✓ import { run } from 'data-mocks-server';

✗ const { run } = require('data-mocks-server'); // Valid CJS, but ESM is preferred in modern TS/JS projects.

The `run` function is the primary entry point for starting the mock server. While CommonJS `require` works, ESM `import` is recommended for TypeScript and modern JavaScript environments.

createExpressApp

✓ import { createExpressApp } from 'data-mocks-server';

✗ import createExpressApp from 'data-mocks-server'; // Not a default export.

Use `createExpressApp` if you need direct access to the underlying Express application instance for custom middleware or advanced configurations, rather than letting `run` manage the server lifecycle.

Mock

✓ import type { Mock } from 'data-mocks-server';

When working with TypeScript, import types like `Mock`, `HttpMock`, or `Response` using `import type` for clarity and to avoid bundling type definitions.

This quickstart demonstrates how to set up a mock server with default HTTP GET endpoints for users and products, including dynamic responses and delays. It also defines two scenarios ('emptyUsers' and 'errorProduct') that can be activated via the built-in UI to override default behaviors, and customizes the port and UI path.

import { run } from 'data-mocks-server'; const server = run({ default: [ { url: '/api/users', method: 'GET', response: { data: [{ id: 1, name: 'Alice' }, { id: 2, name: 'Bob' }] }, delay: 500 // Simulate network latency }, { url: '/api/products/:id', method: 'GET', response: (request) => { const productId = request.params.id; return { status: 200, data: { id: productId, name: `Product ${productId}`, price: 19.99 } }; }, headers: { 'X-Custom-Header': 'Mocked-Response' } } ], scenarios: { emptyUsers: [ { url: '/api/users', method: 'GET', response: { data: [] } } ], errorProduct: [ { url: '/api/products/:id', method: 'GET', response: { status: 500, data: { message: 'Internal Server Error' } } } ] }, options: { port: 4000, uiPath: '/admin-mocks' } }); console.log('Mock server running on http://localhost:4000'); console.log('Admin UI available at http://localhost:4000/admin-mocks'); // To stop the server programmatically (e.g., in tests) // setTimeout(() => { // server.kill(() => console.log('Mock server stopped.')); // }, 10000);

Debug

Known issues

breakingThe API for defining mock responses underwent a significant change in version 9.3.2. Existing `response` configurations from prior versions may no longer be compatible.

fix

Review the new `Response` API documentation and update your mock definitions accordingly. The `response` property may now accept a function or a more structured object for status, headers, and data.

affects: >=9.3.2

breakingVersion 10.0.0 introduced a breaking change as indicated by 'Force package upgrade' and a reference to the v9.3.2 changes. While specific new API changes in 10.0.0 itself aren't detailed, upgrading from pre-9.3.2 versions directly to 10.0.0 will certainly encounter the response API changes.

fix

Always consult the changelog for major version bumps. If migrating from pre-9.3.2, ensure all response configurations are updated to the new format.

affects: >=10.0.0

gotchaThe `v9.3.2` release was initially marked as 'Deprecated' with a note 'Published to incorrect version'. While functionally fixed, users might have encountered temporary issues with that specific version number in their package managers or registries.

fix

Always use the latest stable patch release (e.g., `^10.0.0`) to ensure you're on the most recent, non-deprecated version. If you specifically installed `9.3.2`, consider upgrading.

affects: =9.3.2

gotchaBy default, the server runs on port 3000 and the UI is accessible at the root path '/'. If another service is already using port 3000, the server will fail to start. Also, if your application has a root path handler, it might conflict with the mock server UI.

fix

Configure a different `port` or `uiPath` in the `options` object when calling `run`. For example, `{ options: { port: 4000, uiPath: '/_mocks' } }`.

affects: >=1.0.0

Errors

Common errors & fixes

Error: listen EADDRINUSE: address already in use :::3000

Another process is already using the default port (3000) where data-mocks-server attempts to start.

fix

Specify a different port in the `options` object: `run({ ..., options: { port: 4000 } })`.

TypeError: Cannot read properties of undefined (reading 'data') OR response.status is not a function

You are using an old `response` object structure (pre-v9.3.2) after upgrading to a newer version that changed the response API.

fix

Update your mock `response` definitions. Instead of `{ data: {...} }`, use `{ status: 200, data: {...}, headers: {...} }` or return an object with these properties from a response function.

Cannot find name 'run'.

Incorrect import statement or missing TypeScript configuration to recognize the module as ESM.

fix

Ensure you are using `import { run } from 'data-mocks-server';` in ESM contexts. If using CommonJS, `const { run } = require('data-mocks-server');`. For TypeScript, verify your `tsconfig.json` includes `"moduleResolution": "NodeNext"` or `"Node"` and `"esModuleInterop": true`.

Upgrade

Version history

10.0.2latest on npm

Audit

Dependencies

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Agent activity

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Resources

githubhttps://github.com/kenneth-gray/data-mocks-server ↗

packagehttps://www.npmjs.com/package/data-mocks-server ↗

homepagehttps://www.mock-server.com ↗