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Using Storybook with Go frontends

Storybook [0] is an open source tool for building UI components and pages in isolation.

[0]

I've used it with lots of React projects, where it's been a great way to build out layouts and to allow developers to share, document, and preview components in isolation.

However, it's not just for React. Storybook also supports server-side rendered components [1].

[1]

Configuring storybook

Once Storybook Server has been installed using `npx`, it must be configured to point at a HTTP endpoint that returns HTML.

To connect Storybook Server to a local Go server that's listening on port 60606, we'd place that URL into the `.storybook/preview.js` file.

export const parameters = { 
  server: { 
    url: "http://localhost:60606/storybook_preview"
  }
};

Storybook must also be configured to list the components that it can find, and any parameters that will be passed to the server-side rendered component.

For example, with a simple header `templ` [2] component, we'd need to tell Storybook server that the `name` parameter can be configured.

{% templ headerTemplate(name string) %}
	<header data-testid="headerTemplate">
		<h1>{%= name %}</h1>
	</header>
{% endtempl %}

[2]

To do this, we have to put a `{componentName}.stories.json` file in the `stories` directory, e.g. `headerTemplate`.

The `title` field contains the name of the component.

The `parameters/server/id` field contains the HTTP path of where the `headerTemplate` will be rendered by the backend. This is added to the `url` defined in the `.storybook/preview.js` file, so for this configuration, Storybook will send a HTTP request to `http://localhost:60606/storybook_preview/headerTemplate

The `args` section contains a map of the template's parameter names to default values. The example `headerTemplate` accepts a `name` parameter that is rendered within the `<h1>` element, so the map contains `"name": "Page Name"`.

The `argTypes` section defines the type of input that Storybook will use to render to allow users to edit the value of the parameters in the preview.

Finally, the `stories` section contains pre-configured variants of the template. I've just left a `Default` story which uses the default `args` to render the component.

{
  "title": "headerTemplate",
  "parameters": {
    "server": {
      "id": "headerTemplate"
    }
  },
  "args": {
    "name": "Page Name"
  },
  "argTypes": {
    "name": {
      "control": "text"
    }
  },
  "stories": [
    {
      "name": "Default",
      "Args": {}
    }
  ]
}

Storybook Server can then be started by running `npm run storybook` which starts a Node.js server. However, without a Go server running to render the component, there's nothing to see.

Storybook Server can also be built into a static website which includes the config using the `npm run build-storybook` command. This outputs to a directory called `storybook-static`.

Go server

For each component, Storybook Server sends a HTTP request to the server configured in the `preview.js` file.

Any `args` configured in each `*.stories.json` file are passed as querystring parameters, so the `headerTemplate` in the example above sends a request to `http://localhost:60606/storybook_preview/headerTemplate?name=Page+Name`

The Go server then needs to respond to this request with HTML.

It's then easy to setup a web server, and a custom HTTP handler to do that for each component.

func main() {
	http.HandleFunc("/storybook_preview/headerTemplate", headerTemplateHandler)
	http.ListenAndServe(":60606", nil)
}

func headerTemplateHandler(w http.ResponseWriter, r *http.Request) {
	// Read the name from the querystring.
	name := r.URL.Query().Get("name")
	// Render the component.
	templ.Handler(headerTemplate(name)).ServeHTTP(w, r)
}

With Storybook Server, and the Go server running at the same time, you can get dynamic previews [3].

[3]

Making it easier

There's a few steps to all of this.

Install Storybook Server.
Create `*.stories.json` file for each component.
Run the Storybook Server.
Create a Go server.
Create a HTTP handler for each component.
Run the Go server.

When you add a new component, or change its parameters, you've also got to remember to rebuild and restart the Storybook Server.

I wanted to make this really easy in `templ`, so I created a `storybook` package that downloads and installs Storybook if required, configures the stories, builds the static storybook when required, and starts a local Go server that handles the rendering, and hosting of the Storybook.

This can be coupled with hot reloading tools like air [4] to get it to rebuild [5].

[4]

[5]

All of the Storybook example code is at [6]

[6]

The first thing is to export the Storybook configuration from the component library:

[7]

package example

import (
	"github.com/a-h/templ/storybook"
)

func Storybook() *storybook.Storybook {
	s := storybook.New()
	s.AddComponent("headerTemplate", headerTemplate, 
		storybook.TextArg("name", "Page Name"))
	s.AddComponent("footerTemplate", footerTemplate)
	return s
}

Then, it's possible to make an executable for local execution that imports it [8]. Running this program will download Storybook, configure it, and run it.

[8]

package main

import (
	"context"
	"fmt"
	"os"

	"github.com/a-h/templ/storybook/example"
)

func main() {
	s := example.Storybook()
	if err := s.ListenAndServeWithContext(context.Background()); err != nil {
		fmt.Println(err.Error())
		os.Exit(1)
	}
}

Hosting it in AWS

Creating a Storybook is great, but it's most useful when you can share it with others, so I put together a way to host it in AWS.

The new App Runner service is a good choice for lightweight applications like this, and it's easy to bundle everything up, but it costs a minimum of $5 a month, so I spent a bit of time to rework it to run in Lambda so that people wouldn't be put off by the cost.

The first thing was to create a Lambda function to run the code.

Creating a Lambda function

The local executable does lots of work when `ListenAndServe` is called. Including downloading Storybook and configuring it. This isn't good inside a Lambda function, because it will happen every time the Lambda container is resarted (a cold start), so the process is split into a build step that downloads and configures Storybook, and a run Lambda function that collects the build output and runs it.

[9]

First, the program imports the `example` component library, and calls the `Storybook` function to get all of the configuration.

The `build` function does all of the downloading and configuration of Storybook. This has to be executed before deployment.

var s = example.Storybook()

func build() {
	if err := s.Build(context.Background()); err != nil {
		fmt.Println(err)
		os.Exit(1)
	}
}

Go has a brilliant feature where you can embed entire directories, or individual files, into variables by using a special `go:embed` comment.

This makes it really easy to replace serving files from disk on the local web server with serving files straight out of RAM.

// Embed the build output into the Lambda.
// The build output is only 4MB, so there's plenty of space.
//go:embed storybook-server/storybook-static
var storybookStatic embed.FS

func run() {
	// Replace the filesystem handler with the embedded data.
	rooted, _ := fs.Sub(storybookStatic, "storybook-server/storybook-static")
	s.StaticHandler = http.FileServer(http.FS(rooted))
	// Start a Lambda handler.
	lambda.Start(handler)
}

The Storybook handler is a standard Go HTTP handler, so I wrote a function to map from an `APIGatewayV2HTTPRequest` to a HTTP request, and from a HTTP response back to an `APIGatewayV2HTTPResponse`.

func handler(ctx context.Context, e events.APIGatewayV2HTTPRequest) (resp events.APIGatewayV2HTTPResponse, err error) {
	// Record the result.
	w := httptest.NewRecorder()
	u := e.RawPath
	if len(e.RawQueryString) > 0 {
		u += "?" + e.RawQueryString
	}
	r := httptest.NewRequest(e.RequestContext.HTTP.Method, u, nil)
	s.ServeHTTP(w, r)

	// Convert it to an API Gateway response.
	result := w.Result()
	resp.StatusCode = result.StatusCode
	bdy, err := ioutil.ReadAll(w.Result().Body)
	if err != nil {
		return
	}
	resp.Body = string(bdy)
	if len(result.Header) > 0 {
		resp.Headers = make(map[string]string, len(result.Header))
		for k := range result.Header {
			v := result.Header.Get(k)
			resp.Headers[k] = v
		}
	}
	cookies := result.Cookies()
	if len(cookies) > 0 {
		resp.Cookies = make([]string, len(cookies))
		for i := 0; i < len(cookies); i++ {
			resp.Cookies[i] = cookies[i].String()
		}
	}
	return
}

All that was left was to make it possible to run either the `build` or the `run` (default) operation.

func main() {
	if len(os.Args) < 2 {
		run()
	}
	switch os.Args[1] {
	case "build":
		build()
	case "run":
		run()
	default:
		fmt.Printf("unexpected command %q\n", os.Args[1])
		os.Exit(1)
	}
}

CDK deployment

With a Lambda function handler, I could create a HTTP endpoint to serve up the Storybook using CDK [10].

[10]

The CDK takes care of building the Go function.

bundlingOptions := &awslambdago.BundlingOptions{
	GoBuildFlags: &[]*string{jsii.String(`-ldflags "-s -w"`)},
}
f := awslambdago.NewGoFunction(stack, jsii.String("storybookHandler"), &awslambdago.GoFunctionProps{
	Runtime:    awslambda.Runtime_GO_1_X(),
	Entry:      jsii.String("../lambda"),
	Bundling:   bundlingOptions,
	MemorySize: jsii.Number(1024),
	Timeout:    awscdk.Duration_Millis(jsii.Number(15000)),
})

And then, adding a HTTP API Gateway to call the Lambda function is just a few lines of code.

fi := awsapigatewayv2integrations.NewLambdaProxyIntegration(&awsapigatewayv2integrations.LambdaProxyIntegrationProps{
	Handler:              f,
	PayloadFormatVersion: awsapigatewayv2.PayloadFormatVersion_VERSION_2_0(),
})
endpoint := awsapigatewayv2.NewHttpApi(stack, jsii.String("storybookHttpApi"), &awsapigatewayv2.HttpApiProps{
	DefaultIntegration: fi,
})

This pops out a HTTPS link on the Internet. I like to output the URL at the end so I can see where to visit.

awscdk.NewCfnOutput(stack, jsii.String("storybookEndpointUrl"), &awscdk.CfnOutputProps{
	ExportName: jsii.String("storybookEndpointUrl"),
	Value:      endpoint.Url(),
})

I've hosted it up at [11]

[11]