sveld

sveld generates TypeScript definitions for Svelte components by statically analyzing their props, events, slots and more. Prop types and signatures can be defined using JSDoc notation. This documentation generator can also emit component documentation in Markdown and JSON output formats.

The purpose of this project is to make third party Svelte component libraries compatible with the Svelte Language Server and TypeScript with minimal effort required by the author. For example, TypeScript definitions may be used during development via intelligent code completion in Integrated Development Environments (IDE) like VSCode.

Carbon Components Svelte uses this library to auto-generate component types and API metadata:

• TypeScript definitions: Component TypeScript definitions
• Component Index: Markdown file documenting component props, slots, and events
• Component API: Component API metadata in JSON format

Please note that the generated TypeScript definitions require Svelte version 3.55 or greater.

Given a Svelte component, sveld can infer basic prop types to generate TypeScript definitions compatible with the Svelte Language Server:

Button.svelte

<script>
  export let type = "button";
  export let primary = false;
</script>

<button {...$$restProps} {type} class:primary on:click>
  <slot>Click me</slot>
</button>

The generated definition extends the official SvelteComponentTyped interface exported from Svelte.

Button.svelte.d.ts

import type { SvelteComponentTyped } from "svelte";
import type { SvelteHTMLElements } from "svelte/elements";

type $RestProps = SvelteHTMLElements["button"];

type $Props = {
  /**
   * @default "button"
   */
  type?: string;

  /**
   * @default false
   */
  primary?: boolean;

  [key: `data-${string}`]: any;
};

export type ButtonProps = Omit<$RestProps, keyof $Props> & $Props;

export default class Button extends SvelteComponentTyped<
  ButtonProps,
  { click: WindowEventMap["click"] },
  { default: {} }
> {}

Sometimes, inferring prop types is insufficient.

Prop/event/slot types and signatures can be augmented using JSDoc notations.

/** @type {"button" | "submit" | "reset"} */
export let type = "button";

/**
 * Set to `true` to use the primary variant
 */
export let primary = false;

The accompanying JSDoc annotations would generate the following:

import type { SvelteHTMLElements } from "svelte/elements";

type $RestProps = SvelteHTMLElements["button"];

type $Props = {
  /**
   * @default "button"
   */
  type?: "button" | "submit" | "reset";

  /**
   * Set to `true` to use the primary variant
   * @default false
   */
  primary?: boolean;
};

export type ButtonProps = Omit<$RestProps, keyof $Props> & $Props;

export default class Button extends SvelteComponentTyped<
  ButtonProps,
  { click: WindowEventMap["click"] },
  { default: {} }
> {}

Table of Contents

• Approach
• Usage
  • Installation
  • Rollup
  • Node.js
  • CLI
  • Publishing to NPM
• Available Options
• API Reference
  • @type
  • @typedef
  • @slot
  • @event
  • @restProps
  • @extends
  • @generics
  • @component comments
• Contributing
• License

Approach

sveld uses the Svelte compiler to statically analyze Svelte components exported from a library to generate documentation useful to the end user.

Extracted metadata include:

• props
• slots
• forwarded events
• dispatched events
• $$restProps

This library adopts a progressively enhanced approach. Any property type that cannot be inferred (e.g., "hello" is a string) falls back to "any" to minimize incorrectly typed properties or signatures. To mitigate this, the library author can add JSDoc annotations to specify types that cannot be reliably inferred. This represents a progressively enhanced approach because JSDocs are comments that can be ignored by the compiler.

Usage

Installation

Install sveld as a development dependency.

# npm
npm i -D sveld

# pnpm
pnpm i -D sveld

# Bun
bun i -D sveld

# Yarn
yarn add -D sveld

Rollup

Import and add sveld as a plugin to your rollup.config.js.

// rollup.config.js
import svelte from "rollup-plugin-svelte";
import resolve from "@rollup/plugin-node-resolve";
import sveld from "sveld";

export default {
  input: "src/index.js",
  output: {
    format: "es",
    file: "lib/index.mjs",
  },
  plugins: [svelte(), resolve(), sveld()],
};

When building the library, TypeScript definitions are emitted to the types folder by default.

Customize the output folder using the typesOptions.outDir option.

The following example emits the output to the dist folder:

sveld({
+  typesOptions: {
+    outDir: 'dist'
+  }
})

The tests/e2e folder contains example set-ups:

• single-export: library that exports one component
• single-export-default-only: library that exports one component using the concise export { default } ... syntax
• multi-export: multi-component library without JSDoc annotations (types are inferred)
• multi-export-typed: multi-component library with JSDoc annotations
• multi-export-typed-ts-only: multi-component library that only generates TS definitions
• glob: library that uses the glob strategy to collect/analyze *.svelte files
• carbon: full carbon-components-svelte example

CLI

The CLI wraps the Rollup plugin and uses the "svelte" field defined in your package.json as the entry point.

npx sveld

Append --json or --markdown flags to generate documentation in JSON/Markdown formats, respectively.

npx sveld --json --markdown

Node.js

You can also use sveld programmatically in Node.js.

If no input is specified, sveld will infer the entry point based on the package.json#svelte field.

const { sveld } = require("sveld");
const pkg = require("./package.json");

sveld({
  input: "./src/index.js",
  glob: true,
  markdown: true,
  markdownOptions: {
    onAppend: (type, document, components) => {
      if (type === "h1")
        document.append("quote", `${components.size} components exported from ${pkg.name}@${pkg.version}.`);
    },
  },
  json: true,
  jsonOptions: {
    outFile: "docs/src/COMPONENT_API.json",
  },
});

jsonOptions.outDir

If json is true, a COMPONENT_API.json file will be generated at the root of your project. This file contains documentation for all components.

Use the jsonOptions.outDir option to specify the folder for individual JSON files to be emitted.

sveld({
  json: true,
  jsonOptions: {
    // an individual JSON file will be generated for each component API
    // e.g. "docs/Button.api.json"
    outDir: "docs",
  },
});

Publishing to NPM

TypeScript definitions are outputted to the types folder by default. Don't forget to include the folder in your package.json when publishing the package to NPM.

{
  "svelte": "./src/index.js",
  "main": "./lib/index.mjs",
+ "types": "./types/index.d.ts",
  "files": [
    "src",
    "lib",
+   "types",
  ]
}

Available Options

By default, only TypeScript definitions are generated.

To generate documentation in Markdown and JSON formats, set markdown and json to true.

sveld({
+  markdown: true,
+  json: true,
})

API Reference

@type

Without a @type annotation, sveld will infer the primitive type for a prop:

export let kind = "primary";
// inferred type: "string"

Use the @type tag to explicitly document the type. In the following example, the kind property has an enumerated (enum) type.

Signature:

/**
 * Optional description
 * @type {Type}
 */

Example:

/**
 * Specify the kind of button
 * @type {"primary" | "secondary" | "tertiary"}
 */
export let kind = "primary";

/**
 * Specify the Carbon icon to render
 * @type {typeof import("carbon-icons-svelte").CarbonIcon}
 */
export let renderIcon = Close20;

@typedef

The @typedef tag can be used to define a common type that is used multiple times within a component. All typedefs defined in a component will be exported from the generated TypeScript definition file.

Signature:

/**
 * @typedef {Type} TypeName
 */

Example:

/**
 * @typedef {string} AuthorName
 * @typedef {{ name?: AuthorName; dob?: string; }} Author
 */

/** @type {Author} */
export let author = {};

/** @type {Author[]} */
export let authors = [];

@slot

Use the @slot tag for typing component slots. Note that @slot is a non-standard JSDoc tag.

Descriptions are optional for named slots. Currently, the default slot cannot have a description.

Signature:

/**
 * @slot {Type} slot-name [slot description]
 */

Omit the `slot-name` to type the default slot.

/**
 * @slot {Type}
 */

Example:

<script>
  /**
   * @slot {{ prop: number; doubled: number; }}
   * @slot {{}} title
   * @slot {{ prop: number }} body - Customize the paragraph text.
   */

  export let prop = 0;
</script>

<h1>
  <slot {prop} doubled={prop * 2} />
  <slot name="title" />
</h1>

<p>
  <slot name="body" {prop} />
</p>

@event

Use the @event tag to type dispatched events. An event name is required and a description optional.

Use null as the value if no event detail is provided.

Signature:

/**
 * @event {EventDetail} eventname [event description]
 */

Example:

/**
 * @event {{ key: string }} button:key
 * @event {null} key – Fired when `key` changes.
 */

export let key = "";

import { createEventDispatcher } from "svelte";

const dispatch = createEventDispatcher();

$: dispatch("button:key", { key });
$: if (key) dispatch("key");

Output:

export default class Component extends SvelteComponentTyped<
  ComponentProps,
  {
    "button:key": CustomEvent<{ key: string }>;
    /** Fired when `key` changes. */ key: CustomEvent<null>;
  },
  {}
> {}

@restProps

sveld can pick up inline HTML elements that $$restProps is forwarded to. However, it cannot infer the underlying element for instantiated components.

You can use the @restProps tag to specify the element tags that $$restProps is forwarded to.

Signature:

/**
 * Single element
 * @restProps {tagname}
 *
 * Multiple elements
 * @restProps {tagname-1 | tagname-2 | tagname-3}
 */

Example:

<script>
  /** @restProps {h1 | button} */
  export let edit = false;

  import Button from "../";
</script>

{#if edit}
  <Button {...$$restProps} />
{:else}
  <h1 {...$$restProps}><slot /></h1>
{/if}

@extends

In some cases, a component may be based on another component. The @extends tag can be used to extend generated component props.

Signature:

/**
 * @extends {<relative path to component>} ComponentProps
 */

Example:

/** @extends {"./Button.svelte"} ButtonProps */

export const secondary = true;

import Button from "./Button.svelte";

@generics

Currently, to define generics for a Svelte component, you must use generics attribute on the script tag. Note that this feature is experimental and may change in the future.

However, the generics attribute only works if using lang="ts"; the language server will produce an error if generics is used without specifying lang="ts".

<!-- This causes an error because `lang="ts"` must be used. -->
<script generics="Row extends DataTableRow = any"></script>

Because sveld is designed to support JavaScript-only usage as a baseline, the API design to specify generics uses a custom JSDoc tag @generics.

Signature:

/**
 * @generics {GenericParameter} GenericName
 */

Example

/**
 * @generics {Row extends DataTableRow = any} Row
 */

The generated TypeScript definition will resemble the following:

export default class Component<Row extends DataTableRow = any> extends SvelteComponentTyped<
  ComponentProps<Row>,
  Record<string, any>,
  Record<string, any>
> {}

For a parameter list, the name should be comma-separated but not include spaces.

/**
 * @generics {Param1, Param2} Name1,Name2
 */

export default class Component<Param1, Param2> extends SvelteComponentTyped<
  ComponentProps<Name1, Name2>,
  Record<string, any>,
  Record<string, any>
> {}

@component comments

The Svelte Language Server supports component-level comments through the following syntax: <!-- @component [comment] -->.

sveld will copy these over to the exported default component in the TypeScript definition.

Example:

<!-- @component
@example
<Button>
  Text
</Button>
-->
<button>
  <slot />
</button>

Output:

/**
 * @example
 * <Button>
 *   Text
 * </Button>
 */
export default class Button extends SvelteComponentTyped<ButtonProps, {}, { default: {} }> {}

Contributing

Refer to the contributing guidelines.

License

Apache-2.0