# Request id

Every request passed through this interceptor, has an id. **This doesn't mean its a UNIQUE
ID**.

Each request id are responsible for binding a request to its cache, for referencing (or
invalidating) it later and to make the interceptor treat each request with the same id as
the same request.

The id generation is good enough to generate the same id for theoretically sames requests.
A simple example is a request with `{ baseURL: 'https://a.com/', url: '/b' }` results to
the same id with `{ url: 'https://a.com/b/' }`.

> If you send two completely different requests with the same id, the interceptor will
> treat them as the same request, sharing its cache and every other as.

```js #runkit
const axios = require('axios');
const { setupCache } = require('axios-cache-interceptor');

// Global
setupCache(axios);

const { id } = await axios.get('https://jsonplaceholder.typicode.com/posts/1', {
  baseURL: 'baseURL',
  query: { name: 'value' }
});

// Generated
console.log('Id 1: ' + id);
console.log('Cache 1:', await axios.storage.get(id));

const { id: id2 } = await axios.get('https://jsonplaceholder.typicode.com/posts/1', {
  id: 'my-overridden-id'
});

// Specified
console.log('Id 2: ' + id2);
console.log('Cache 2:', await axios.storage.get(id2));
```

The
[default](https://github.com/arthurfiorette/axios-cache-interceptor/blob/main/src/util/key-generator.ts)
id generation can clarify this idea.

## Joining requests

Two requests will be treated as the same if they have the same `id` property. If it was
not defined, it will be auto generated by the provided `Key Generator`.

You can override their `id` property by providing a custom one.

```js
const response = await axios.get('url', {
  id: 'my overridden id'
});

// Response.id always returns the resolved it for the specific request. (In this case, 'my overridden id')
response.id === 'my overridden id';
```

## Custom generator

Everything that is used to treat two requests as same or not, is done by the `generateKey`
property.

The value is hashed into a signed integer when the returned value from the provided
generator is not a `string` or a `number`.

By default, it uses the `method`, `baseURL`, `params`, `data` and `url` properties from
the request object into an hash code generated by the
[`object-code`](https://www.npmjs.com/package/object-code) library.

If you need to change or share the cache for two requests based on other properties, like
headers and etc, you can create your own Key Generator:

```js
const generator = buildKeyGenerator(({ headers = {} }) => {
  // In this imaginary example, two requests will
  // be treated as the same if their x-cache-server header is the same.
  return headers['x-cache-server'] || 'not-set';
});

const axios = mockAxios({
  generateKey: generator
});
```