data-mocks
v4.1.0
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data-mocks
Library (written in TypeScript) to mock REST and GraphQL requests
Why is this library useful
When developing web applications locally, it is not uncommon to request data from an API. However, the API might not actually exist yet, or we might want to control what the responses are.
Typically, this sort of problem has been solved by either writing a separate mock API service alongside the project (i.e. having a Node service running locally with your application) or creating a development database that replicates staging or production environments. Both of these approaches are heavy and can lead to using incorrect data if schemas are out of sync.
This library aims to allow rapid local development without the dependency of a database or fully implemented APIs.
Setup
- Either
npm install data-mocks
oryarn add data-mocks
- Optional: extract the scenario from URL using the imported
extractScenarioFromLocation()
function- Or you can just hardcode a string to pass through instead
- Import
injectMocks()
function into your project withimport { injectMocks } from 'data-mocks'
- Create an array of
Scenario
's you would like to use (see examples) - Pass array of
Scenario
's toinjectMocks()
- Hooray, all HTTP requests to mocked endpoints will now respond with the mocked data you have specified
Integration patterns
Regardless of framework or CLI tool used to generate your project, integrating data-mocks
into your project is easy. Here are how it may look for you:
React
import React from 'react';
import ReactDOM from 'react-dom';
import App from './App';
async function main() {
if (process.env.NODE_ENV === 'development') {
const { injectMocks, extractScenarioFromLocation } = await import(
'data-mocks'
);
// You could just define your mocks inline if you didn't want to import them.
const { getMocks } = await import('./path/to/your/mock/definitions');
injectMocks(getMocks(), extractScenarioFromLocation(window.location));
}
ReactDOM.render(<App />, document.getElementById('root'));
}
main();
Angular
import { enableProdMode } from '@angular/core';
import { platformBrowserDynamic } from '@angular/platform-browser-dynamic';
import { AppModule } from './app/app.module';
import { environment } from './environments/environment';
async function setupMocks() {
const { injectMocks, extractScenarioFromLocation } = await import(
'data-mocks'
);
// You could just define your mocks inline if you didn't want to import them.
const { getMocks } = await import('./path/to/your/mock/definitions');
injectMocks(getMocks(), extractScenarioFromLocation(window.location));
}
}
async function main() {
if (environment.production) {
enableProdMode();
}
if (!environment.production) {
await setupMocks();
}
platformBrowserDynamic()
.bootstrapModule(AppModule)
.catch((err) => console.error(err));
}
main();
No framework (just vanilla JS)
async function main() {
if (process.env.NODE_ENV === 'development') {
const { injectMocks, extractScenarioFromLocation } = await import(
'data-mocks'
);
// You could just define your mocks inline if you didn't want to import them.
const { getMocks } = await import('./path/to/your/mock/definitions');
injectMocks(getMocks(), extractScenarioFromLocation(window.location));
}
}
main();
In these examples, we dynamically import data-mocks
and our mock definitions as to not increase production bundle sizes (given that we will never need/want to use these files in production environments).
It is not a requirement to dynamically import data-mocks
or your mock definitions - it is just a recommendation :)
REST + GraphQL
data-mocks
works with either REST or GraphQL requests. It is also possible to easily mock both in the same application.
See the examples below to see how this is done.
Examples
Basic mock injection without scenarios
import { injectMocks } from 'data-mocks';
import axios from 'axios';
const scenarios = {
default: [
{
url: /login/,
method: 'POST',
response: { some: 'good response' },
responseCode: 200,
},
{
url: /some-other-endpoint/,
method: 'GET',
response: { another: 'response' },
responseCode: 200,
delay: 1000,
},
{
url: /endpoint-with-headers/,
method: 'GET',
response: { same: 'response' },
responseHeaders: { token: 'mock-token' },
responseCode: 200,
},
],
};
injectMocks(scenarios);
fetch('http://foo.com/login', { method: 'POST', body: {} })
.then((response) => response.json())
.then((myJson) => console.log(myJson)); // resolves with { some: 'good response' } after a 200ms delay
fetch('http://foo.com/some-other-endpoint')
.then((response) => response.json())
.then((myJson) => console.log(myJson)); // resolves with { another: 'response' } after a 1 second delay
axios
.post('http://foo.com/login', {})
.then((response) => console.log(response)); // resolves with { another: 'response' } after a 200ms delay
axios
.get('http://foo.com/some-other-endpoint')
.then((response) => console.log(response)); // resolves with { another: 'response' } after a 1 second delay
In this example, we define a default scenario in our scenarios
map. The Scenario objects are described by the Scenario interface. We then inject the scenarios into our application via the injectMocks() function. Finally, when we use fetch / XHR to make a request to endpoints that match our scenario objects, the mocked responses are returned.
N.B
In the above example we are using axios
as our XHR library of choice. However
data-mocks
will work with any library that uses XMLHttpRequest
under the hood.
Mock injection with scenarios
import { injectMocks, extractScenarioFromLocation } from 'data-mocks';
import axios from 'axios';
const scenarios = {
default: [
{
url: /login/,
method: 'POST',
response: { some: 'good response' },
responseCode: 200,
},
{
url: /some-other-endpoint/,
method: 'GET',
response: { another: 'response' },
responseCode: 200,
delay: 1000,
},
],
failedLogin: [
{
url: /login/,
method: 'POST',
response: { some: 'bad things happened' },
responseCode: 401,
},
],
};
injectMocks(scenarios, 'failedLogin');
fetch('http://foo.com/login', { method: 'POST', body: {} }).then((response) =>
console.log(response)
); // resolves with a 401 after a 200ms delay
fetch('http://foo.com/some-other-endpoint').then((response) =>
console.log(response)
); // resolves with { another: 'response' } after a 1 second delay
axios
.post('http://foo.com/login', {})
.then((response) => console.log(response)); // resolves with a 401 after a 200ms delay
axios
.get('http://foo.com/some-other-endpoint')
.then((response) => console.log(response)); // resolves with { another: 'response' } after a 1 second delay
In this example, if we load our site up with ?scenario=failedLogin
in the querystring and then attempt to hit the login
endpoint, it will fail with a 401. However, the some-other-endpoint
endpoint will still respond with the response in the default
scenario as we have not provided one in the failedLogin
scenario.
Basic GraphQL mock injection
Here, we have a React application using urql
as a GraphQL client. This shows how GraphQL queries work and it can be assumed that if you want to use REST mocks in this application, you can do so as you normally would (see examples above).
In reality, the mock definitions would live at a higher level (like the entrypoint into the application) where they could be injected only if we were in development mode.
import React from 'react';
import { injectMocks, extractScenarioFromLocation } from 'data-mocks';
import gql from 'graphql-tag';
const mocks = {
default: [
{
url: /graphql/,
method: 'GRAPHQL',
operations: [
{
operationName: 'Query',
type: 'query',
response: { data: { test: 'test' } },
},
{
operationName: 'Mutation',
type: 'mutation',
response: { data: { test: 'test' } },
},
],
},
],
};
injectMocks(mocks, extractScenarioFromLocation(window.location));
const Component = () => {
const [result] = useQuery({ query: Query }); // result will be { data: { test: 'test' } }
return <>{result.data.test}</>;
};
Exported types
Scenarios
| Property | Type | Required | Description | | ---------- | ------ | -------- | ------------------------------------------------------------------------------------------------- | | default | Mock[] | ✅ | The default scenario mapping. Provides a default set of mocked responses. | | [scenario] | Mock[] | ❌ | Additional scenario mappings. The key is the name of the scenario and is what is used in the URL. |
HttpMock
| Property | Type | Required | Description | | --------------- | ---------------- | -------- | -------------------------------------------------------------------- | | url | RegExp | ✅ | Regular expression that matches part of the URL. | | method | string | ✅ | HTTP method matching one of 'GET', 'POST', 'PUT', 'PATCH', 'DELETE'. | | response | object | string | ✅ | Body of the response. | | responseCode | number | ❌ | Response code. Defaults to 200. | | responseHeaders | object | ❌ | Response headers. Defaults to empty. | | delay | number | ❌ | Delay (in milliseconds) before response is returned. Defaults to 0. |
GraphQLMock
| Property | Type | Required | Description | | ---------- | ------------------ | -------- | --------------------------------------------------------- | | url | RegExp | ✅ | Regular expression that matches part of the URL. | | method | string | ✅ | Must be 'GRAPHQL' to specify that this is a GraphQL mock. | | operations | Array<Operation> | ✅ | Array of GraphQL operations for this request. |
Mock
Union type of HttpMock
and GraphQLMock
.
Operation
| Property | Type | Required | Description |
| --------------- | ------ | -------- | ------------------------------------------------------------------- |
| type | string | ✅ | GraphQL operation type. Must be either query
or mutation
. |
| operationName | string | ✅ | GraphQL operation name. |
| response | object | ✅ | Body of the response. |
| responseCode | number | ❌ | Response code. Defaults to 200. |
| responseHeaders | object | ❌ | Response headers. Defaults to empty. |
| delay | number | ❌ | Delay (in milliseconds) before response is returned. Defaults to 0. |
MockConfig
| Property | Type | Required | Description | | ------------------------------ | ------- | -------- | ------------------------------------------------------------------------------------------------------------------ | | allowXHRPassthrough | boolean | ❌ | Any unmatched routes for XHR will pass through to the actual endpoint, rather than be mocked. Defaults to false. | | allowFetchPassthrough | boolean | ❌ | Any unmatched routes for fetch will pass through to the actual endpoint, rather than be mocked. Defaults to false. | | disableConsoleWarningsForFetch | boolean | ❌ | When enabled, this will suppress any console warnings generated by fetch-mock fallbacks |
Exported functions
injectMocks
| Parameter | Type | Required | Description |
| --------- | ------------------------------- | -------- | --------------------------------------------------------------------------- |
| scenarios | Scenarios[] | ✅ | A mapping of scenarios and their responses |
| scenario | keyof Scenarios[] | ❌ | The scenario to run. Defaults to default
|
| config | MockConfig | ❌ | Config object that allows for different behaviour of how mocks are injected |
extractScenarioFromLocation
| Parameter | Type | Required | Description |
| --------- | --------------------------------------------------------------------- | -------- | ---------------------------------------------------------------------------------------------------------------- |
| location | Location | ✅ | The browser location object. The value for the scenario
part of the querystring will be extracted and returned |
Gotchas
- GraphQL operations must have an operation name.