@podium/podlet v5

A Module for building page fragment servers in a micro frontend architecture.

See the official Podium documentation site.

This is a module for building a podlet server. A podlet server is responsible for generating HTML fragments which can then be used in a @podium/layout server to compose a full HTML page.

This module can be used together with a plain node.js HTTP server or any HTTP framework and any templating language of your choosing (or none if you prefer).

Note: Connect compatible middleware based frameworks (such as Express) are considered first class in Podium so this module provides a .middleware() method for convenience.

For writing podlet servers with other HTTP frameworks, the following modules also exist:

[Fastify Podlet Plugin]
Hapi Podlet Plugin
[Koa Podlet Plugin]

Installation

$ npm install @podium/podlet

Getting started

Building a simple podlet server using Express.

import express from 'express';
import Podlet from '@podium/podlet';

// create a new podlet instance
const podlet = new Podlet({
    name: 'myPodlet',
    version: '1.3.1',
    pathname: '/',
    development: true,
});

// create a new express app instance
const app = express();

// mount podlet middleware in express app
app.use(podlet.middleware());

// create a route to serve the podlet's manifest file
app.get(podlet.manifest(), (req, res) => {
    res.json(podlet);
});

// create a route to serve the podlet's content
app.get(podlet.content(), (req, res) => {
    res.podiumSend(`<div>hello world</div>`);
});

// start the app on port 7100
app.listen(7100);

API Documentation

Constructor

Create a new podlet instance.

const podlet = new Podlet(options);

options

option	type	default	required
name	`string`		✓
version	`string`		✓
pathname	`string`		✓
manifest	`string`	`/manifest.json`
content	`string`	`/`
fallback	`string`
logger	`object`
development	`boolean`	`false`
useShadowDOM	`boolean`	`false`

name

The name the podlet identifies itself by. This value can contain upper and lower case letters, numbers, the - character and the _ character. No spaces. When shadow DOM is used, either via the useShadowDOM constructor option or via the wrapWithShadowDOM method, the name must comply with custom element naming rules. See MDN for more information.

Example:

const podlet = new Podlet({
    name: 'myPodlet';
});

version

The current version of the podlet. It is important that this value be updated when a new version of the podlet is deployed since the page (layout) that the podlet is displayed in uses this value to know whether to refresh the podlet's manifest and fallback content or not.

Example:

const podlet = new Podlet({
    version: '1.1.0';
});

pathname

Pathname for where a Podlet is mounted in an HTTP server. It is important that this value matches where the entry point of a route is in an HTTP server since this value is used to define where the manifest is for the podlet.

If the podlet is mounted at the "root", set pathname to /:

const app = express();
const podlet = new Podlet({
    name: 'myPodlet',
    version: '1.0.0',
    pathname: '/',
});

app.use(podlet.middleware());

app.get('/', (req, res, next) => {
    [ ... ]
});

If the podlet is to be mounted at /foo, set pathname to /foo and mount middleware and routes at or under /foo

const app = express();
const podlet = new Podlet({
    name: 'myPodlet',
    version: '1.0.0',
    pathname: '/foo',
});

app.use('/foo', podlet.middleware());

app.get('/foo', (req, res, next) => {
    [ ... ]
});

app.get('/foo/:id', (req, res, next) => {
    [ ... ]
});

manifest

Defines the pathname for the manifest of the podlet. Defaults to /manifest.json.

The value should be relative to the value set on the pathname argument. In other words if a Podlet is mounted into an HTTP server at /foo and the manifest is at /foo/component.json, set pathname and manifest as follows:

const app = express();
const podlet = new Podlet({
    name: 'myPodlet',
    version: '1.0.0',
    pathname: '/foo',
    manifest: '/component.json',
});

app.get('/foo/component.json', (req, res, next) => {
    [ ... ]
});

The value can be a relative URL and the .manifest() method can be used to retrieve the value after it has been set.

content

Defines the pathname for the content of the Podlet. Defaults to /.

The value should be relative to the value set on the pathname argument. In other words if a podlet is mounted into an HTTP server at /foo and the content is at /foo/index.html, set pathname and content as follows:

const app = express();
const podlet = new Podlet({
    name: 'myPodlet',
    version: '1.0.0',
    pathname: '/foo',
    content: '/index.html',
});

app.get('/foo/index.html', (req, res, next) => {
    [ ... ]
});

The value can be a relative or absolute URL and the .content() method can be used to retrieve the value after it has been set.

fallback

Defines the pathname for the fallback of the Podlet. Defaults to an empty string.

The value should be relative to the value set with the pathname argument. In other words if a Podlet is mounted into an HTTP server at /foo and the fallback is at /foo/fallback.html, set pathname and fallback as follows:

const app = express();
const podlet = new Podlet({
    name: 'myPodlet',
    version: '1.0.0',
    pathname: '/foo',
    fallback: '/fallback.html',
});

app.get('/foo/fallback.html', (req, res, next) => {
    [ ... ]
});

The value can be a relative or absolute URL and the .fallback() method can be used to retrieve the value after it has been set.

logger

Any log4j compatible logger can be passed in and will be used for logging. Console is also supported for easy test / development.

Example:

const podlet = new Podlet({
    logger: console;
});

Under the hood abslog is used to abstract out logging. Please see abslog for further details.

development

Turns development mode on or off. See the section about development mode.

useShadowDOM

Turns declarative shadow DOM encapsulation on for the podlet. When enabled, the podlet content will be wrapped inside a declarative shadow DOM wrapper to isolate it from the rest of whichever page it is being included on.

const podlet = new Podlet({ ..., useShadowDOM: true });

Please note the following caveats when using this feature:

You must name your podlet following custom element naming conventions as explained here: https://developer.mozilla.org/en-US/docs/Web/API/CustomElementRegistry/define#valid_custom_element_names
In order to style your content, you will need to include your CSS inside the shadow DOM wrapper. You can do this using one of the following 2 options:

You can include a <style> tag before your content

res.podiumSend(`
	<style>
		...styles here...
	</style>
	<div>...content here...</div>
`);

You can have your podlet CSS included for you by using the "shadow-dom" scope

podlet.css({ value: '/path/to/css', scope: 'shadow-dom' });
res.podiumSend(`
	<div>...content here...</div>
`);

For more fine grained control, you can use the podlet.wrapWithShadowDOM method directly

const podlet = new Podlet({ ..., useShadowDOM: false });

const wrapped = podlet.wrapWithShadowDOM(`<div>...content here...</div>`);
res.podiumSend(`
	${wrapped}
`);

Podlet Instance

The podlet instance has the following API:

.process(HttpIncoming, options)

Method for processing a incoming HTTP request. This method is intended to be used to implement support for multiple HTTP frameworks and in most cases will not need to be used directly by library users to create podlet servers.

What it does:

Handles detection of development mode and sets appropriate defaults
Runs context deserializing on the incoming request and sets a context object at HttpIncoming.context.

Returns an HttpIncoming object.

The method takes the following arguments:

HttpIncoming (required)

An instance of the HttpIncoming class.

import { HttpIncoming } from '@podium/utils';
import Podlet from '@podium/podlet';

const podlet = new Podlet({
    name: 'myPodlet',
    version: '1.0.0',
    pathname: '/',
});

app.use(async (req, res, next) => {
    const incoming = new HttpIncoming(req, res, res.locals);
    try {
        await podlet.process(incoming);
        if (!incoming.proxy) {
            res.locals.podium = result;
            next();
        }
    } catch (error) {
        next(error);
    }
});

options

option	default	type	required	details
proxy	`true`	`boolean`	`false`	If `@podium/proxy` should be applied as part of the `.process()` method

.middleware()

A Connect compatible middleware function which takes care of the multiple operations needed for a podlet to operate correctly. This function is more or less a wrapper for the .process() method.

Important: This middleware must be mounted before defining any routes.

Example:

const app = express();
app.use(podlet.middleware());

Returns an Array of internal middleware that performs the tasks described above.

.manifest(options)

This method returns the value of the manifest argument that has been set on the constructor.

Examples:

Set the manifest using the default pathname which is /manifest.json:

const app = express();
const podlet = new Podlet({
    name: 'myPodlet',
    version: '1.0.0',
    pathname: '/',
});

app.get(podlet.manifest(), (req, res) => { ... });

Set the manifest using /component.json:

const app = express();
const podlet = new Podlet({
    name: 'myPodlet',
    version: '1.0.0',
    pathname: '/foo',
    manifest: '/component.json',
});

app.get(podlet.manifest(), (req, res) => { ... });

Podium expects the podlet's manifest route to return a JSON document describing the podlet. This can be achieved by simply serializing the podlet object instance.

Example:

const app = express();
app.get(podlet.manifest(), (req, res) => {
    res.status(200).json(podlet);
});

The route will then respond with something like:

{
    "name": "myPodlet",
    "version": "1.0.0",
    "content": "/",
    "fallback": "/fallback",
    "css": [],
    "js": [],
    "proxy": {}
}

options

option	type	default	required
prefix	`boolean`	`false`

prefix

Sets whether the method should prefix the return value with the value for pathname that was set in the constructor.

Examples:

return the full pathname to the manifest (/foo/component.json):

const app = express();
const podlet = new Podlet({
    name: 'myPodlet',
    version: '1.0.0',
    pathname: '/foo',
    manifest: '/component.json',
});

podlet.manifest({ prefix: true });

.content(options)

This method returns the value of the content argument set in the constructor.

Examples:

Set the content using the default pathname (/):

const app = express();
const podlet = new Podlet({
    name: 'myPodlet',
    version: '1.0.0',
    pathname: '/',
});

app.get(podlet.content(), (req, res) => { ... });

Set the content path to /index.html:

const app = express();
const podlet = new Podlet({
    name: 'myPodlet',
    version: '1.0.0',
    pathname: '/foo',
    content: '/index.html',
});

app.get(podlet.content(), (req, res) => { ... });

Set the content path to /content and define multiple sub-routes each taking different URI parameters:

const app = express();
const podlet = new Podlet({
    name: 'myPodlet',
    version: '1.0.0',
    pathname: '/',
    content: '/content',
});

app.get('/content', (req, res) => { ... });
app.get('/content/info', (req, res) => { ... });
app.get('/content/info/:id', (req, res) => { ... });

options

option	type	default	required
prefix	`boolean`	`false`

prefix

Specifies whether the method should prefix the return value with the pathname value that was set in the constructor.

Examples:

return the full pathname to the content (/foo/index.html):

const app = express();
const podlet = new Podlet({
    name: 'myPodlet',
    version: '1.0.0',
    pathname: '/foo',
    content: '/index.html',
});

podlet.content({ prefix: true });

The prefix will be ignored if the returned value is an absolute URL.

.fallback(options)

This method returns the value of the fallback argument set in the constructor.

Examples:

Set the fallback to /fallback.html:

const app = express();
const podlet = new Podlet({
    name: 'myPodlet',
    version: '1.0.0',
    pathname: '/',
    fallback: '/fallback.html',
});

app.get(podlet.fallback(), (req, res) => { ... });

options

option	type	default	required
prefix	`boolean`	`false`

prefix

Specifies whether the fallback method should prefix the return value with the value for pathname set in the constructor.

Examples:

Return the full pathname to the fallback (/foo/fallback.html):

const app = express();
const podlet = new Podlet({
    name: 'myPodlet',
    version: '1.0.0',
    pathname: '/foo',
    fallback: '/fallback.html',
});

podlet.fallback({ prefix: true });

The prefix will be ignored if the returned value is an absolute URL.

.js(options)

Sets the pathname for a podlet's javascript assets.

options can be either an object or an array of options objects as described below.

When a value is set it will be internally kept and used when the podlet instance is serialized into a manifest JSON string.

In addition, JS information will be serialized into a Link header and sent as an HTTP 103 early hint with content and fallback responses so that the layout client can get access to assets before the main podlet body. The layout can use this information to generate 103 early hints for the browser so that the browser can begin downloading asset files while still waiting for the podlet and layout bodys.

options

option	type	default
value	`string`
prefix	`boolean`	`false`
type	`string`	`default`

value

Used to set the pathname for the podlets JavaScript assets. This value can be a URL at which the podlet's user facing JavaScript is served. The value can be either the pathname of a URL or an absolute URL.

Examples:

Serve a javascript file at /assets/main.js:

const app = express();
const podlet = new Podlet({
    name: 'myPodlet',
    version: '1.0.0',
    pathname: '/',
});

podlet.js({ value: '/assets/main.js' });

// or

podlet.js([{ value: '/assets/main.js' }, { value: '/assets/secondary.js' }]);

Serve assets statically along side the app and set a relative URI to the JavaScript file:

const app = express();
const podlet = new Podlet({
    name: 'myPodlet',
    version: '1.0.0',
    pathname: '/',
});

app.use('/assets', express.static('./app/files/assets'));
podlet.js({ value: '/assets/main.js' });

Set an absolute URL to where the javascript file is located:

const podlet = new Podlet({
    name: 'myPodlet',
    version: '1.0.0',
    pathname: '/',
});

podlet.js({ value: 'http://cdn.mysite.com/assets/js/e7rfg76.js' });

prefix

Specify whether the method should prefix the return value with the value for pathname that was set in the constructor.

Examples:

Return the full pathname, /foo/assets/main.js, to the JavaScript assets:

const app = express();
const podlet = new Podlet({
    name: 'myPodlet',
    version: '1.0.0',
    pathname: '/foo',
});

podlet.js({ value: '/assets/main.js', prefix: true });

Prefix will be ignored if the returned value is an absolute URL.

type

Set the type of script which is set. default indicates an unknown type. module inidcates as ES6 module.

.css(options)

Sets the options for a podlet's CSS assets.

options can be either an object or an array of options objects as described below.

When a value is set it will be internally kept and used when the podlet instance is serialized into a manifest JSON string.

In addition, CSS information will be serialized into a Link header and sent as an HTTP 103 early hint with content and fallback responses so that the layout client can get access to assets before the main podlet body. The layout can use this information to generate 103 early hints for the browser so that the browser can begin downloading asset files while still waiting for the podlet and layout bodys.

options

option	type	default	required
value	`string`
prefix	`boolean`	`false`

value

Used to set the pathname for the CSS assets for the Podlet. The value can be a URL at which the podlet's user facing CSS is served. The value can be the pathname of a URL or an absolute URL.

The value can be set only once. If called multiple times with a value, the method will throw. The method can be called multiple times to retrieve the value however.

Examples:

Serve a CSS file at /assets/main.css:

const app = express();
const podlet = new Podlet({
    name: 'myPodlet',
    version: '1.0.0',
    pathname: '/',
});

podlet.css({ value: '/assets/main.css' });

// or

podlet.css([{ value: '/assets/main.css' }, { value: '/assets/secondary.css' }]);

Serve assets from a static file server and set a relative URI to the CSS file:

const app = express();
const podlet = new Podlet({
    name: 'myPodlet',
    version: '1.0.0',
    pathname: '/',
});

app.use('/assets', express.static('./app/files/assets'));
podlet.css({ value: '/assets/main.css' });

Set an absolute URL to where the CSS file is located:

const podlet = new Podlet({
    name: 'myPodlet',
    version: '1.0.0',
    pathname: '/',
});

podlet.css({ value: 'http://cdn.mysite.com/assets/css/3ru39ur.css' });

prefix

Sets whether the method should prefix the return value with the value for pathname set in the constructor.

Examples:

Return the full pathname (/foo/assets/main.css) to the CSS assets:

const app = express();
const podlet = new Podlet({
    name: 'myPodlet',
    version: '1.0.0',
    pathname: '/foo',
});

podlet.css({ value: '/assets/main.css', prefix: true });

Prefix will be ignored if the returned value is an absolute URL.

.proxy({ target, name })

Method for defining proxy targets to be mounted by the @podium/proxy module in a layout server. It's worth mentioning that this will not mount a proxy in the server where the podlet instance is used.

Proxying is intended to be used as a way to make podlet endpoints public. A common use case for this is creating endpoints for client side code to interact with (ajax requests from the browser). One might also make use of proxying to pass form submissions from the browser back to the podlet.

This method returns the value of the target argument and internally keeps track of the value of target for use when the podlet instance is serialized into a manifest JSON string.

In a podlet it is possible to define up to 4 proxy targets and each target can be the pathname part of a URL or an absolute URL.

For each podlet, each proxy target must have a unique name.

Examples:

Mounts one proxy target /api with the name api:

const app = express();
app.get(podlet.proxy({ target: '/api', name: 'api' }), (req, res) => { ... });

Defines multiple endpoints on one proxy target /api with the name api:

const app = express();
app.get('/api', (req, res) => { ... });
app.get('/api/foo', (req, res) => { ... });
app.post('/api/foo', (req, res) => { ... });
app.get('/api/bar/:id', (req, res) => { ... });

podlet.proxy({ target: '/api', name: 'api' });

Sets a remote target by defining an absolute URL:

podlet.proxy({ target: 'http://remote.site.com/api/', name: 'remoteApi' });

Knowing where proxy endpoints are mounted in a layout

When proxy targets are mounted in a layout server they are namespaced to avoid proxy targets from multiple podlets conflicting with each other.

This can cause a proxy endpoint in a podlet to have different pathnames in different layout servers if the podlet is included in multiple layout servers.

Information regarding where proxy endpoints are mounted in any given layout can be found by inspecting the publicPathname key of the @podium/context for each request made to the podlet by a layout.

By combining publicPathname and mountOrigin from the @podium/context object, it is possible to build absolute URLs to a podlet's proxy endpoints.

Example:

This example demonstrates a podlet server that exposes one HTTP POST endpoint which will be made publicly available through a proxy in a layout and one content endpoint which supplies an HTML form that, when submitted, will make a POST request to the HTTP POST endpoint we defined.

const app = express();
const podlet = new Podlet({ ... });

// route serving the manifest
app.get(podlet.manifest(), (req, res) => {
    res.status(200).json(podlet);
});

// this give us, among others, the context
app.use(podlet.middleware());

// route recieving the submitted form made public by proxying
app.post(podlet.proxy({ target: '/api', name: 'api' }), (req, res) => { ... });

// content route serving an HTML form
app.get(podlet.content(), (req, res) => {
    const ctx = res.locals.podium.context;
    res.podiumSend(`
        <form action="${ctx.mountOrigin}${ctx.publicPathname}/api" method="post">
            [ ... ]
        </form>
    `)
});

app.listen(7100);

res.podiumSend(fragment)

Method on the http.ServerResponse object for sending an HTML fragment. Calls the send / write method on the http.ServerResponse object.

When in development mode this method will wrap the provided fragment in a default HTML document before dispatching. When not in development mode, this method will just dispatch the fragment.

Example of sending an HTML fragment:

app.get(podlet.content(), (req, res) => {
    res.podiumSend('<h1>Hello World</h1>');
});

.defaults(context)

Alters the default context set when in development mode.

By default this context has the following shape:

{
    debug: 'false',
    locale: 'en-EN',
    deviceType: 'desktop',
    requestedBy: 'the_name_of_the_podlet',
    mountOrigin: 'http://localhost:port',
    mountPathname: '/same/as/manifest/method',
    publicPathname: '/same/as/manifest/method',
}

The default development mode context can be overridden by passing an object with the desired key / values to override.

Example of overriding deviceType:

const podlet = new Podlet({
    name: 'foo',
    version: '1.0.0',
});

podlet.defaults({
    deviceType: 'mobile',
});

Additional values not defined by Podium can also be appended to the default development mode context in the same way.

Example of adding a context value:

const podlet = new Podlet({
    name: 'foo',
    version: '1.0.0',
});

podlet.defaults({
    token: '9fc498984f3ewi',
});

N.B. The default development mode context will only be appended to the response when the constructor argument development is set to true.

.view(template)

Override the default encapsulating HTML document when in development mode.

Takes a function in the following shape:

podlet.view(data => `<!doctype html>
<html lang="${data.locale}">
    <head>
        <meta charset="${data.encoding}">
        <title>${data.title}</title>
        <link href="${data.css}" rel="stylesheet">
        <script src="${title.js}" defer></script>
        ${title.head}
    </head>
    <body>
        ${title.body}
    </body>
</html>`;
);

Development mode

In most cases podlets are fragments of a whole HTML document. When a layout server is requesting a podlet's content or fallback, the podlet should serve just that fragment and not a whole HTML document with its <html>, <head> and <body>. It is also the case that when a layout server is requesting a podlet it provides a context.

These things can prove challenging for local development since accessing a podlet directly, from a web browser, in local development will render the podlet without either an encapsulating HTML document or a Podium context that the podlet might need to function properly.

To solve this it is possible to switch a podlet to development mode by setting the development argument in the constructor to true.

When in development mode a default context on the HTTP response will be set and an encapsulating HTML document will be provided (so long as res.podiumSend() is used) when dispatching the content or fallback.

The default HTML document for encapsulating a fragment will reference the values set on .css() and .js() and use locale from the default context to set language on the document.

The default context in development mode can be altered by the .defaults() method of the podlet instance.

The default encapsulating HTML document used in development mode can be replaced by the .view() method of the podlet instance.

Note: Only turn on development mode during local development, ensure it is turned off when in production.

Example of turning on development mode only in local development:

const podlet = new Podlet({
    development: process.env.NODE_ENV !== 'production';
});

When a layout server sends a request to a podlet in development mode, the default context will be overridden by the context from the layout server and the encapsulating HTML document will not be applied.

License

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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.github/workflows		.github/workflows
example		example
lib		lib
tests		tests
types		types
.editorconfig		.editorconfig
.gitattributes		.gitattributes
.gitignore		.gitignore
.npmrc		.npmrc
.prettierrc.json		.prettierrc.json
CHANGELOG.md		CHANGELOG.md
LICENSE		LICENSE
README.md		README.md
eslint.config.js		eslint.config.js
fixup.js		fixup.js
package.json		package.json
release.config.js		release.config.js
renovate.json		renovate.json
tsconfig.json		tsconfig.json
tsconfig.test.json		tsconfig.test.json

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podium-lib/podlet

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@podium/podlet v5

Installation

Getting started

API Documentation

Constructor

options

name

version

pathname

manifest

content

fallback

logger

development

useShadowDOM

Podlet Instance

.process(HttpIncoming, options)

HttpIncoming (required)

options

.middleware()

.manifest(options)

options

prefix

.content(options)

options

prefix

.fallback(options)

options

prefix

.js(options)

options

value

prefix

type

.css(options)

options

value

prefix

.proxy({ target, name })

Knowing where proxy endpoints are mounted in a layout

res.podiumSend(fragment)

.defaults(context)

.view(template)

Development mode

License

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