--- parts: - Overview - Ajax - Tools title: 'Ajax: Overview' eleventyNavigation: key: Tools >> Ajax >> Overview title: Overview order: 10 parent: Tools >> Ajax --- # Ajax: Overview `Ajax` is a small wrapper around `fetch` which: - Allows globally registering request and response interceptors - Throws on 4xx and 5xx status codes - Supports caching, so a request can be prevented from reaching to network, by returning the cached response. - Supports JSON with `ajax.fetchJson` by automatically serializing request body and deserializing response payload as JSON, and adding the correct Content-Type and Accept headers. - Adds accept-language header to requests based on application language - Adds XSRF header to request if the cookie is present and the request is for a mutable action (POST/PUT/PATCH/DELETE) and if the origin is the same as current origin or the request origin is in the xsrfTrustedOrigins list. ## Installation ```bash npm i --save @lion/ajax ``` ### Relation to fetch `Ajax` delegates all requests to fetch. `ajax.fetch` and `ajax.fetchJson` have the same function signature as `window.fetch`, you can use any online resource to learn more about fetch. [MDN](http://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch) is a great start. ## `ajax.fetch` The `fetch` method of `ajax` is a very small wrapper around native `window.fetch` and returns a native [`Response`](https://developer.mozilla.org/en-US/docs/Web/API/Response) object, the main differences with native `window.fetch` are: - it will use any caching options that you've configured in the `Ajax` class - it will throw on response statuses between 400 and 600 (native fetch doesn't throw) - it will run any interceptors that you've configured - it will add a XSRF header to the request if the XSRF cookie is present Otherwise, you can expect the same usage as from `window.fetch`. Here are some simple examples: ```js // A simple GET request const response = await ajax.fetch('/api/foo'); const data = await response.json(); // or .text(), .clone(), .formData(), etc ``` ```js // A simple POST request const response = await ajax.fetch('/api/foo', { method: 'POST', body: JSON.stringify({ foo: 'bar' }), }); ``` ## `ajax.fetchJson` The `fetchJson` method of `ajax` has some additional features, added for convenience and ease of use. For example, the `fetchJson` method: - adds the `accept` header with a value of `application/json` - adds the `content-type` header with a value of `application/json`, if a request body is provided - automatically `JSON.stringifies` the request body, if one is provided - will attempt to parse the response body as JSON if available - and also automatically remove a JSON prefix from the response body if one is configured > Note that instead of returning only a [`Response`](https://developer.mozilla.org/en-US/docs/Web/API/Response), `fetchJson` returns an object containing the [`Response`](https://developer.mozilla.org/en-US/docs/Web/API/Response) and a `JSON.parse`'d `body` ```js // A simple GET request const { response, body } = await ajax.fetchJson('/api/foo'); // body.foo === 'bar'; ``` ```js // A simple POST request const { response, body } = await ajax.fetchJson('/api/foo', { method: 'POST', body: { foo: 'bar' }, }); ``` ## Interceptors Interceptors are functions that can be used to inspect or modify the [`Request`](https://developer.mozilla.org/en-US/docs/Web/API/Request) or `Response` objects of a network request. ### Request interceptors A request interceptor is a function that takes a [`Request`](https://developer.mozilla.org/en-US/docs/Web/API/Request) object, and returns a [`Request`](https://developer.mozilla.org/en-US/docs/Web/API/Request) object, or a [`Response`](https://developer.mozilla.org/en-US/docs/Web/API/Response) object, and runs _before_ the native `window.fetch` call is done, allowing you to modify or inspect a request before it's made. If you return a [`Response`](https://developer.mozilla.org/en-US/docs/Web/API/Response) object, the response will be returned by the `fetch` or `fetchJson` methods, instead of passing the `Request` to the native `window.fetch` function. Returning a [`Request`](https://developer.mozilla.org/en-US/docs/Web/API/Request): ```js function addAcceptLanguage(request) { request.headers.set('accept-language', 'EN_GB'); return request; } ajax.addRequestInterceptor(addAcceptLanguage); ``` Returning a [`Response`](https://developer.mozilla.org/en-US/docs/Web/API/Response): ```js function interceptFooRequest(request) { if (request.headers.get('foo')) { return Response.json({ foo: 'bar' }); } return request; } ajax.addRequestInterceptor(interceptFooRequest); ``` Request interceptors can be async and will be awaited. ### Response interceptors A response interceptor is a function that takes a [`Response`](https://developer.mozilla.org/en-US/docs/Web/API/Response) object, and returns a [`Response`](https://developer.mozilla.org/en-US/docs/Web/API/Response) object, and runs _after_ the native `window.fetch` call is done, allowing you to modify or inspect the response before it's returned by `fetch`/`fetchJson`. ```js async function rewriteFoo(response) { const body = await response.clone().text(); return new Response(body.replaceAll('foo', 'bar'), response); } ajax.addResponseInterceptor(rewriteFoo); ``` Response interceptors can be async and will be awaited. ### Response JSON object interceptors A response JSON object interceptor is a function that takes a successfully parsed response JSON object and `response` object and returns a new response JSON object. It's used only when the request is made with the `fetchJson` method, providing a convenience API to directly modify or inspect the parsed JSON without the need to parse it and handle errors manually. ```js async function interceptJson(jsonObject, response) { if (response.url === '/my-api') { return { ...jsonObject, changed: true, }; } return jsonObject; } ajax.addResponseJsonInterceptor(interceptJson); ``` Response JSON object interceptors can be async and will be awaited. ## Ajax class options | Property | Type | Default Value | Description | | -------------------------------- | -------- | ------------------------------------------------------------------ | ----------------------------------------------------------------------------------------------------------------------------------------------------------- | | addAcceptLanguage | boolean | `true` | Whether to add the Accept-Language header from the `data-localize-lang` document property | | addCaching | boolean | `false` | Whether to add the cache interceptor and start storing responses in the cache, even if `cacheOptions.useCache` is `false` | | xsrfCookieName | string | `"XSRF-TOKEN"` | The name for the Cross Site Request Forgery cookie | | xsrfHeaderName | string | `"X-XSRF-TOKEN"` | The name for the Cross Site Request Forgery header | | xsrfTrustedOrigins | string[] | [] | List of trusted origins, the XSRF header will also be added if the origin is in this list. | | jsonPrefix | string | `""` | The prefix to add to add to responses for the `.fetchJson` functions | | cacheOptions.useCache | boolean | `false` | Whether to use the default cache interceptors to cache requests | | cacheOptions.getCacheIdentifier | function | a function returning the string `_default`. | A function to determine the cache that should be used for each request; used to make sure responses for one session are not used in the next. Can be async. | | cacheOptions.methods | string[] | `["get"]` | The HTTP methods to cache reponses for. Any other method will invalidate the cache for this request, see "Invalidating cache", below | | cacheOptions.maxAge | number | `360000` | The time to keep a response in the cache before invalidating it automatically | | cacheOptions.invalidateUrls | string[] | `undefined` | Urls to invalidate each time a method not in `cacheOptions.methods` is encountered, see "Invalidating cache", below | | cacheOptions.invalidateUrlsRegex | regex | `undefined` | Regular expression matching urls to invalidate each time a method not in `cacheOptions.methods` is encountered, see "Invalidating cache", below | | cacheOptions.requestIdFunction | function | a function returning the base url and serialized search parameters | Function to determine what defines a unique URL | | cacheOptions.contentTypes | string[] | `undefined` | Whitelist of content types that will be stored to or retrieved from the cache | | cacheOptions.maxResponseSize | number | `undefined` | The maximum response size in bytes that will be stored to or retrieved from the cache | | cacheOptions.maxCacheSize | number | `undefined` | The maxiumum total size in bytes of the cache; when the cache gets larger it is truncated | ## Caching ```js import { ajax, createCacheInterceptors } from '@lion/ajax'; // Note: getCacheIdentifier can be async const getCacheIdentifier = () => { let userId = localStorage.getItem('lion-ajax-cache-demo-user-id'); if (!userId) { localStorage.setItem('lion-ajax-cache-demo-user-id', '1'); userId = '1'; } return userId; }; const TEN_MINUTES = 1000 * 60 * 10; // in milliseconds const cacheOptions = { useCache: true, maxAge: TEN_MINUTES, }; const { cacheRequestInterceptor, cacheResponseInterceptor } = createCacheInterceptors( getCacheIdentifier, cacheOptions, ); ajax.addRequestInterceptor(cacheRequestInterceptor); ajax.addResponseInterceptor(cacheResponseInterceptor); ``` Or use a custom cache object and add the cache config to the constructor: ```js import { Ajax } from '@lion/ajax'; const storeButDontRetrieveByDefaultConfig = { addCaching: true, cacheOptions: { getCacheIdentifier, useCache: false, maxAge: TEN_MINUTES, }, }; const customAjax = new Ajax(storeButDontRetrieveByDefaultConfig); ``` ### Invalidating the cache Invalidating the cache, or cache busting, can be done in multiple ways: - Going past the `maxAge` of the cache object - Changing cache identifier (e.g. user session or active profile changes) - Doing a non GET request to the cached endpoint - Invalidates the cache of that endpoint - Invalidates the cache of all other endpoints matching `invalidatesUrls` and `invalidateUrlsRegex` ### Restricting what to cache The library has a number of options available to restrict what should be cached. They include: #### By content type `cacheOptions.contentTypes` If this option is set, it is interpreted as a whitelist for which content types to cache. The content types of a given response is derived from its `Content-Type` header. If this option is set, responses that do not have a `Content-Type` header are never added to or retrieved from the cache. #### By response size `cacheOptions.maxResponseSize` This option sets a maximum size (in bytes) for a single response to be cached. The size of the response is determined first by looking at the `Content-Length` header; if this header is not available, the response is inspected (through the `blob()` function) and its size retrieved. ### Limiting the cache size `cacheOptions.maxCacheSize` This option sets a maximum size (in bytes) for the whole cache. The size of a response is determined first by looking at the `Content-Length` header; if this header is not available, the response is inspected (through the `blob()` function) and its size retrieved. If the cache grows larger than the `maxCacheSize` option, the cache is truncated according to a First-In-First-Out (FIFO) algorithm that simply removes the oldest entries until the cache is smaller than `options.maxCacheSize`.