changelog.md

ChangeLog

8.0.0-alpha.3 (2023-06-11)

• #476: When cache: no-store is specified on fetch() functions, Ketting will now no longer store responses with a Content-Location in its internal cache.
• #477: When storing responses with Content-Location, bodies are now cloned before storing so callees can still read the date.
• Testing Node 20.

8.0.0-alpha.2 (2023-04-11)

• Added HAL 'name' property to links.
• Updates for changes in Typescript strictness.

8.0.0-alpha.1 (2023-03-16)

• Ketting requires Node 16 now.
• No longer using node-fetch, as fetch() is natively supported on Node 18. If you are using Ketting with Node 16, you should install node-fetch or run node with the --experimental-fetch option.
• Upgraded OAuth2 dependency to @badgateway/oauth2-client.
• Submitting actions with missing required fields will now throw an exception.
• Actions that have pre-filled values will auto submit those values unless they are explicitly overridden.
• #459: Now uses the correct spelling of 'placeholder' in HAL forms (@dayre).
• Export the FetchMiddleware type.
• #444: Allow multiple query parameters to be set with the same key when specifying template variables. (@qmachard)
• Upgrade to Typescript 5

7.5.1 (2022-09-03)

• Typescript 4.8 support!

7.5.0 (2022-08-26)

• #401: The mechanism that de-duplicates identical requests is now a bit smarter, and will not de-duplicate requests that are significantly different such as a different Accept header. (@hugothomas @reda-alaoui)
• #450: value field for some HAL inputs were ignored (color, checkbox, radio).

7.4.2 (2022-05-11)

• Added support for minLength and maxLength attributes on textarea fields in HAL Forms. (@dayre).

7.4.1 (2022-03-21)

Idential to the last beta. Contains the following features that were introduced in the previous betas:

• #433: Fixed race condition when processing nested _embedded resources and emiting update events. The order at which they happen is now consistent. When the update event happens, the entire cache should be up to date.
• #328: Resource.go() and Client.go() can now take a Link object as the argument.

7.4.1-beta.1 (2022-03-20)

• Fixed a bug that was introduced with #433.

7.4.1-beta.0 (2022-03-20)

• #433: Fixed race condition when processing nested _embedded resources and emiting update events. The order at which they happen is now consistent. When the update event happens, the entire cache should be up to date.
• #328: Resource.go() and Client.go() can now take a Link object as the argument.

7.4.0 (2022-03-17)

• #426: Setting up cache dependencies through inv-by links is now possible via HAL _links and in embedded resources, as well as links from all the other formats.
• #425: Fewer warnings related to 'Max listeners exceeded'. The default of 10 is too low for typical Ketting applications.

7.3.0 (2022-01-06)

• #416: Cache-dependencies setup with inv-by links are now respected when manually clearing resource caches.
• #414: Don't attempt to parse the response if it had a 204 status, even if there was a Content-Type header.
• #408: Emit a warning when an _embedded HAL item is missing a good self link.

7.2.0 (2021-08-04)

• #395: Relative URIs in embedded HAL documents are now resolved using the 'self' link in the embedded document, instead of the parent. Although not explicitly said in the HAL standards, I feel this is the right behavior. Most users will not see a difference, but if you relied on the old behavior this could cause some subtle BC breaks.

7.1.1 (2021-06-15)

• #392: The action() function on State classes would only return the default action (@reda-alaoui).
• Changed how Cache classes are exported, as an experiment to see if IDE docs are more complete.

7.1.0 (2021-05-27)

• Support for the inv-by Link relationship type from the Linked Cache Invalidation draft. This link lets a resource tell the client that it's cache should expire when the linked resource's cache also expires.
• The 'prompt' field in HAL Forms for properties with 'options' set was ignored.

7.0.1 (2021-05-04)

• No longer testing Node 10 and Node 15. Added Node 16.
• Actions are now retained when caching. Before this, action information was dropped which meant that any actions in embedded resources were not accessible. (@hugothomas)

7.0.0 (2021-04-11)

• New major version! See Github for a list of changes.
• Title header is now defined as a HTTP Entity Header.

7.0.0-beta.5 (2021-03-08)

• label and value were parsed in reverse.

7.0.0-beta.4 (2021-02-26)

• Added renderAs 'checkbox' to multi-select fields in actions.
• Export OptionDataSource.

7.0.0-beta.3 (2021-02-21)

• Support for HAL Forms version 2021-02-20, which adds the 'options' property.
• Kettings now has support for 'dropdown' fields, allowing users to provide lists of possible options in 3 different ways: 1. An inline list 2. An external HTTP resource (JSON body or CSV body) 3. Provided as links from a hypermedia source. Only 1 and 2 are supported by HAL Forms, 3 is just an internal feature until there is a format that has first-class support for this.
• A bit of a rewrite of 'fields' again. Only a single type is exported, and all the types are cleaned up.

7.0.0-beta.2 (2021-01-25)

• Support for Siren 'title' on fields. This was an oversight.

7.0.0-beta.1 (2021-01-25)

• Remove support for Prefer-Push. Browsers are basically dropping HTTP/2 Push, and not enough work is done to make this very interesting. More background.
• Revert 'unifiying URLs' PR, we're back to using url.resolve in node.

7.0.0-beta.0 (2021-01-19)

• Note: this release has a number of BC breaks, which will only affect you if you wrote custom format parsers. See the wiki for more details.
• #326: State objects now have follow() and followAll() methods.
• #322: Add type, status, detail, instance properties to Problem class, for better support of application/problem+json. (@sazzer).
• #327: If a response is received with a Content-Location header, the response will now immediately get stored in the cache.
• Support for draft-dalal-deprecation-header. Ketting will now emit warnings if a Deprecation header is detected, and will also provide information from the Sunset header and include the uri of the deprecation link relation.
• Support for the latest HAL-Forms features, including target, step, min, max, type, minLength, maxLength, placeholder, cols, rows.
• Support multiple HAL Forms, as per the latest spec updates. Before only a 'default' form was supported.
• Add textarea form field type.
• #324: Only use {cache: 'no-cache'} with .refresh(), not .get().
• Fixed a subtle URL resolving bug in browsers. (Node was not affected).

6.2.0 (2020-12-01)

• Updated fetch-mw-oauth2, which has a few new features: * Fixed a race condition where two 401's in quick succession could result in two OAuth2 refresh requests, ultimately causing 1 to fail. * Preemptively refresh if we know when the access token will expire.

6.1.4 (2020-11-30)

• #302: Templated links without template data don't work.

6.1.3 (2020-11-19)

• Add a getCache() function to Resource, which allows a user to get the latest Resource State in a synchronous manner.
• #292: Parse Siren's 'value' property in action fields.
• fetch-mw-oauth2 dependency had a bug related to refreshing tokens. This release ships with a version without that bug.

6.1.2 (2020-11-09)

• Update the fetch-mw-oauth2 dependency, which adds an onAuthError event.

6.1.1 (2020-11-05)

• state.links.delete() can now take a href argument to delete a specific link from its list.
• Improvements in error messaging.
• Upgrade to Webpack 5

6.1.0 (2020-10-04)

• Large changes in the actions/form system. This should still be considered experimental and could cause some minor BC breaks.
• Actions are now effectively a serialization of a HTML form, and it's now possible to introspect information such as the target, method, contentType, etc.
• Some refactoring in the State objects, simplifiying these significantly.

6.0.4 (2020-10-04)

• State objects now have an actions() method that return all defined actions.

6.0.3 (2020-09-30)

• #241: Add application/prs.hal-forms+json to Accept header and treat as HAL (@reda-alaoui).
• #260: action() could not be successfully called on a HAL action. (@reda-alaoui).
• Add action() function to State interface.

6.0.2 (2020-09-28)

• #248: Parse JSON objects that have an array at the top-level.
• #257: ETag and Last-Modified are now treated as 'Content headers', which means they will get returned from getContentHeaders().

6.0.1 (2020-09-09)

• Quick re-release. Some files were left in the dist/ directory that were not cleaned up.

6.0.0 (2020-09-09)

• New major release!
• Added support for Siren action fields.
• Added support for HAL Forms.

6.0.0-beta.2 (2020-08-15)

• Support draft-nottingham-link-hint on Links.
• Added: client.fetcher.advertiseKetting. Setting this to false will cause Ketting to not set the User-Agent header.
• Resource.patch() will now return a State object if the server responded with 200 OK and a body.

6.0.0-beta.1 (2020-08-10)

• #229: Embedded resources were not cached. (@madsmadsen)
• #230: Respect headers property in options of refresh() function. (@madsmadsen)
• Lots of Ketting 6 doc updates.
• JSDocs everywhere gotten a fresh proof read.

6.0.0-beta.0 (2020-07-06)

• Switched from tslint to eslint.
• Feature complete!

6.0.0-alpha.7 (2020-06-19)

• isState() type guard is exported.

6.0.0-alpha.6 (2020-06-16)

• The Links object now has a default 'context', making it easier to add relative links.
• Links now has an easier to use API for setting or adding new links.
• Links now has a .delete() method to delete by rel.

6.0.0-alpha.5 (2020-06-08)

• Added 'actions', allowing users to automatically submit actions and/or Forms for supported formats.
• Action support is added for text/html and application/vnd.siren+json
• Supported content-types for actions are application/json and application/x-www-form-urlencoded.
• State objects now have a reference to Client.
• resolve() function is now a package export, providing a cross-platform function for resolving urls.
• Resource has now a updateCache function for local state changes without submitting to the server.
• refresh() now emits an update event.

6.0.0-alpha.4 (2020-05-11)

• Fixing bugs related to patch(), post() in the browser build.

6.0.0-alpha.3 (2020-05-10)

• Resources implement EventEmitter, and can emit stale, update and delete events.
• The 'body' property on State is now 'data'
• #141: Added head() function and ability to follow links just through HEAD methods via the Link header.
• Added a NeverCache and ShortCache if automatically storing every State object until invalidation is not desired.
• When calling put() with a new State object, that object will now be placed in cache.
• When refreshing, fetch() is now given the 'reload' cache setting, so that refresh() is a true Refresh, even with a browser cache.
• #130: Support relative bookmark URIs when using Ketting in a browser.
• Siren was not correctly parsed.
• Add .clone() method to all State object.

6.0.0-alpha.2 (2020-05-03)

• State is now exported.
• #184: Added a new postFollow() function that takes over the role of post(). post() is now intended for RPC-like operations and form submissions.

6.0.0-alpha.1 (2020-05-03)

• Re-release. The build contained a few older files that weren't meant to be packaged.

6.0.0-alpha.0 (2020-04-28)

• Big BC-breaking rewrite. Changes are numerous, but the important ones are listed here.
• Resource.get() now returns a State object instead of just a response body. This object has methods to make it easier to manipulate and get information about the response, including links. It's also a stable, non-async object.
• Ketting class is now called Client. It's still exposed as Ketting as well for BC purposes.
• Client.getResource() has been removed. Use Client.go() instead.
• A HTTP Fetch middleware system has been added, for easier manipulation of requests and responses. Middlewares can be added for every request, or for specific origins (domains).
• All authentication settings have been removed, and reimplemented as fetch middlewares. They take roughly the same options, but the setup has changed.
• Resource.get(), Resource.put(), etc. can now all take custom headers and other options to manipulate the request.
• In the past you could just send a body with Resource.post(), .put(), .patch(). Now this body must be a wrapped in an object with at least a .body property. This is an annoying BC break but will allow for more flexibility that was previous impossible.
• Proper support for 'binary' resources.
• Hal Links will now be reserialized on put().
• Resource.link, Resource.links and Resource.hasLink has been deprecated, but not removed.
• Link objects are now a simple typescript type, and no longer implemented as a class.
• FollowerOne is now FollowPromiseOne and FollowerMany is now FollowPromiseMany.
• All things called Representor has been removed, and rewritten with a completely new API. A HAL representor is now a HalState.
• #175: Nested embedded items are now also placed in the cache.

5.2.1 (2020-03-03)

• Use the title= attribute from the HTTP Link header, if it exists.

5.2.0 (2020-02-17)

• Added 'finally()' to custom follower promises.
• All representors are now exported in the representor namespace.

5.1.2 (2020-02-12)

• Correct return type on followAll, so it may be chained with preFetch. This was only an issue when doing 'multiple hops'.

5.1.1 (2020-01-10)

• #173: De-duplicate HAL links if they appear in _embedded and _links.

5.1.0 (2020-01-05)

• Support for the Collection+json format.
• Added a preferTransclude() method on the Follower objects. This automatically adds a Prefer: tranclude="rel" header.

5.0.1 (2019-12-09)

• Update all dependencies.

5.0.0 (2019-11-22)

• This version is the exact same as the previous alpha.

5.0.0-alpha.7 (2019-11-12)

• Added hasLink on Resources and Representations.

5.0.0-alpha.6 (2019-11-06)

• Fixed a bug in getOptions()

5.0.0-alpha.5 (2019-11-06)

• Added a preferPush() method to 'Follower' objects, allowing you to automatically send Prefer-Push headers when following links.
• Moved all functionality related to the 'Repreprentor' in a utility class, making both the Ketting and Resource classes simpler.
• Simplified Resource.refresh(), making it easier to read and do less work.
• When calling .post(), the function will only return a new resource if the HTTP response code was 201.
• If the HTTP response code to a post() call was 205, it will now return the current resource.
• Removed the logic for automatically adding Prefer-Push headers. This was unreliable, and usually did the wrong thing. The new system is 100% opt-in and developer-driven.
• Added Ketting.getOptions() to return a list of options that were passed to Ketting. The options will be enhanced with OAuth2 refresh and access tokens as they become available, meaning that it can be used to place in LocalStorage to remember sessions. This feature is experimental and incomplete. It might change even in minor versions.

5.0.0-alpha.4 (2019-10-31)

• This version is identical to the last, but fixes an issue on npmjs.com. Updating is not needed.

5.0.0-alpha.3 (2019-10-31)

• It's now possible to tell Ketting to prefetch every resource when following links via Resource.follow('foo').preFetch().
• Link and LinkNotFound are now both exported.
• Documentation overhaul.

5.0.0-alpha.2 (2019-10-21)

• Slight tweak to the webpack build, so that other typescript + webpack projects can use the webpack build and use the minified files.

5.0.0-alpha.1 (2019-10-21)

• Now supports the 'invalidates' link rel. When specified in a HTTP response, Ketting will automatically clear the cache of any related resources. See draft-nottingham-linked-cache-inv-04.

5.0.0-alpha.0 (2019-10-18)

• Support for the Siren format.
• Rewrite of the 'representation' system, which is responsible for supporting all the different media types. This results in a few small BC breaks.
• NEW: follow() and followAll() now throw LinkNotFound instead of the generic Error when a link could not be found.
• NEW: Resources now have a link(rel: string) function, which returns a a single Link object.
• BC BREAK: Ketting.getRepresentor() is now Ketting.createRepresentation() and is responsible for constructing the object instead of just returning a constructor.
• BC Break: body, links and embedded on Representor objects are all gone and replaced with getBody(), getLinks() and getEmbedded().
• BUG: Hal is now more lenient with broken responses.
• NEW: Compatible with Typescript's strictNullChecks setting. Overall stronger typing all around.
• NEW: Hal responses from the HAL representor are now properly typed.
• CHANGE: Link chaining system has been rewritten, opening the door to new features that weren't possible before.

4.0.4 (2019-10-31)

• This version is identical to the last, but fixes an issue on npmjs.com. Updating is not needed.

4.0.3 (2019-09-11)

• The internal resource cache will now evict items for any non-safe HTTP method.

4.0.2 (2019-09-05)

• Broke Typescript exports again

4.0.1 (2019-09-05)

• Fix Typescript defintion files so Ketting may be imported correctly.

4.0.0 (2019-09-04)

• #129: Using the package in non-typescript node.js now works with a simple const Ketting = require('ketting').
• #129: Fixed the browser distribution. the Ketting constructor is registered globally again.

4.0.0-alpha.0 (2019-04-22)

• The old format for OAuth2 setup is now no longer supported.
• It's now possible to specify per-domain authentication using wildcards. This allows you to set up specific authentication credentials for specific domains. This might be useful in case you talk to multiple API's with a single client.

3.1.0 (2019-03-28)

• If Ketting anticipates that a user might want to fetch multiple resources in sequence (a follow chain), it will now add Prefer-Push header and a Prefer: transclude header. Both are experimental internet drafts to suggest to a server to do a HTTP/2 push or embed a child resource respecitvely. This feature is experimental and might change as these drafts change.

3.0.2 (2019-03-19)

• A mistake was made when releasing version 3. A branched was not merged in entirely, which caused some of the new OAuth2 features to be partially missing. This has now been corrected.

3.0.1 (2019-03-18)

• Updated dependencies

3.0.0 (2019-03-18)

• Switched OAuth2 implementation from client-oauth2 to fetch-mw-oauth2. This adds support for authorization_code auth, removes 11 dependencies and reduces the minified Ketting build from 69KB to 28KB.
• OAuth2 options now have a new format. The old format is still supported, but will be removed from a future version.
• The baseHref propertyname was renamed to Context on the Link type. The new name matches the name from RFC8288. This is a small BC break.

2.5.1 (2019-03-01)

• #120: The system that de-duplicates identical requests will cache failures forever. This is now fixed. Highly recommended update.

2.5.0 (2019-01-22)

• Basic JSON:API support. Currently only links appearing in the top-level document are supported.
• #113: Support for Typescript environments that don't have esModuleInterop set to true.
• Added a 'go' function for easily getting resources based on relative uris.

2.4.1 (2018-11-07)

• If a link appears in both _embedded and _links, they will be de-duplicated. HAL technically requires links to appear in both places, so scanning _embedded should not be needed. However, most implementations will not add links _links if they were already _embedded. This change caters both usages.

2.4.0 (2018-11-05)

• The Resource class is now a generic typescript type. This allows a user of the library to define specific 'types of resources' and leverage static typing for GET and PUT requests.
• A few documentation updates.

2.3.0 (2018-10-10)

• Better handling of Content-Types. When following HAL links that have a type parameter, the type is rememebered and used in Accept and Content-Type headers, for GET, PUT and POST requests.
• If no type was provided, it will use the last Content-Type header from GET response.
• If that GET request never happened, it uses the first 'default' Content-Type from client.contentTypes, and enumerates all mime-types from that list for Accept headers.
• No longer incorrectly sends text/plain Content-Types.
• Optimization: If multiple calls are made to ask for a Resource's current representation, all these calls are coalesced into one. The big benefit is that there are no longer multiple parallel GET requests.
• Webpack browser build is set to 'production' mode.
• Fixed: After refreshing an OAuth2 token, the new access token wasn't used.

2.2.1 (2018-09-19)

• Refreshing OAuth2 tokens without having a refresh_token. client_credentials in particular shouldn't return a refresh_token, so for these cases, new access tokens are acquired using a new client_credentials request.

2.2.0 (2018-09-18)

• Support for OAuth2 client_credentials grant.

2.1.0 (2018-09-14)

• No longer ships with cross-fetch and whatwg-fetch. To use this library in a browser, you must run this in a browser that supports fetch or provide your own polyfill.
• Updated dependencies

2.0.4 (2018-09-12)

• Fixed bug: HAL title values weren't parsed.

2.0.3 (2018-08-23)

• Exporting 'Resource' for TS purposes.

2.0.2 (2018-08-23)

• Updated dependencies
• Fixed a typescript definition problem.

2.0.1 (2018-06-17)

• Same as last build.

2.0.0 (2018-06-17)

• #71: Total conversion to Typescript.
• BC break: Minified files are now in the browser/ directory, not the dist/ directory.
• #78: Webpack build had a broken version of querystring, which caused Link: header parsing to fail in browsers.
• #80: resource.fetch() would throw an exception with some combinations of arguments.
• #90: get() and refresh() will now throw an Error when a server did not include a content-type.
• #89: Refactored OAuth utility to be a bit more clear.
• #83: Support for resource.patch(). The implementation is pretty basic. Let us know how you would like to use it!

1.1.0 (2018-04-07)

• #70: Moved all source from lib/ to src/. This is prepping for typescript support.
• #73: Mocha tests can now be ran in a browser.
• #76: Fixed a browser bug: Headers is not a constructor.

1.0.0 (2018-03-25)

• #66: Support for Accept header weighing with the q= parameter.
• #68: Updated all dependencies to their latest version.

0.10.3 (2018-01-31)

• #63: It was not possible to expand templated links with variables after more than one chained hop. (@mhum).

0.10.2 (2018-01-31)

• #62: It was not possible to override headers such as Content-Type when calling Resource.fetch(), if these were also set in the fetchInit defaults. (@mhum).

0.10.1 (2018-01-31)

• #60: Chaining more than 2 follow statements did not work.

0.10.0 (2017-11-16)

• #19: Support for OAuth2 access and refresh tokens. When used, the library can automatically refresh the access token if the previous one expired. It can also supports the client_credentials OAuth2 grant (@mhum).

0.9.0 (2017-09-23)

• #52: Now using the new URL object in browsers for resolving relative urls, and falling back to a DOM based url resolving mechanism if it's not available. This causes the browser distribution to drop another 10KB to 46KB.
• Moved a bunch of utility objects into a util/ directory, so it's more clear what the important API's are.
• #55: Fixed another problem related to the fetchInit function in firefox.

0.8.3 (2017-09-10)

• Including the sourcemap file in the NPM distribution.

0.8.2 (2017-09-10)

• #53: Regression related to the new 'fetchInit' option.
• Now generating source maps.

0.8.1 (2017-09-04)

• #50: Allow Fetch settings to be passed to the constructor of Ketting, so that settings such as credentials: include may be passed.

0.8.0 (2017-08-28)

• #49: Removed support for expanding CURIEs in HAL. This was in conflict with the HAL standard. The canonical relation type is the prefix in the REL, not the expanded CURIE uri.

0.7.1 (2017-08-24)

• Lots of documentation updates.
• Including web distribution in NPM package.

0.7.0 (2017-08-21)

• This library is now called Ketting. It used to be called Restl. Ketting is the dutch word for chain.
• Automatically expanding Curies in the HAL _link object.

0.6.0 (2017-08-20)

• #15: Browser support via webpack!
• #45: Removed Bluebird dependency.
• #16: Parsing the HTTP Link header (RFC5988).
• #30: Added support for automatically parsing application/problem+json error responses and throwing better exceptions. (RFC7807).
• #47: Link object now uses an object as its only constructor argument.

0.5.0 (2017-08-08)

• #41: Support for parsing HTML5. The library can now extract link and a elements with rel attributes.
• Removed the accept option. This should now be controlled with the contentTypes property.
• #40: Removed support for the Requests library. This library now only used the Fetch API, to make it compatible with browsers in the future.

0.4.2 (2017-08-03)

• #39: Making it easier to fire off custom HTTP requests on a resource using the Fetch API. You can now just provide the init argument without providing a url.

0.4.1 (2017-07-07)

• #38: Add HTTP response to HTTP-related exceptions.

0.4.0 (2017-07-07)

• #37: Support for templated uris.

0.3.2 (2017-04-27)

• #33: Support for OAuth2 Bearer token.

0.3.1 (2017-04-26)

• #31: Support for setting a standard Content-Type HTTP header.

0.3.0 (2017-04-24)

• #28: Support for Basic Authentication

0.2.1 (2017-04-21)

• #27: Fixed exception messages, they missed the HTTP status code.

0.2.0 (2017-04-21)

• #17: Now using the Fetch API instead of the requests library. The requests library is kept around for BC purposes, but this will eventually be removed.
• #25: the resourceCache was accidentally shared between Client instances.

0.1.2 (2017-04-19)

• #11: Added test framework.
• #11: Added follow() function on Client object for an easy shortcut.

0.1.1 (2017-04-03)

• #10: Returning the response body from the refresh() function, similar to GET but cache-defeating.

0.1.0 (2017-02-13)

• #7: Strip _embedded and _links from Representation.body. They are already available through Representation.embedded and Representation.links.
• Added a cache for resources in the Client object, which ensures that if you request the same resource twice, you'll end up with the same object.
• #6: Automatically parse _embedded and treat items in this object as real resources.
• Fixed a bug in post().
• Allowing custom headers to be set, and allowing default headers to be overridden.
• Automatically resolve all urls from links().

0.0.4 (2017-02-06)

• Bugfixes.
• Linting with eslint.

0.0.3 (2017-02-06)

• Now using Bluebird for promises, so we can extend them.
• #2: Custom requests are now possible on Resource objects.
• #3: Promises returned from follow() now have a follow() function themselves, making it extremely easy to hop from link to link.
• Added a post() method for making new resources. This function returns a Resource object again if the response contained a Location header.
• #4: Things in the _embedded property are now also treated as links and can be followed.
• The links() method on Resource now have a rel argument for easy filtering.
• Added a followAll() function for getting collections.

0.0.2 (2017-01-03)

• PUT request.
• DELETE request.

0.0.1 (2016-12-28)

• First version!
• Parses HAL _links.
• Follows links.
• GET requests.
• refresh() function.