sveld

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 3.31 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.d.ts

/// <reference types="svelte" />
import { SvelteComponentTyped } from "svelte";

export interface ButtonProps extends svelte.JSX.HTMLAttributes<HTMLElementTagNameMap["button"]> {
  /**
   * @default "button"
   */
  type?: string;

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

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:

/// <reference types="svelte" />
import { SvelteComponentTyped } from "svelte";

export interface ButtonProps extends svelte.JSX.HTMLAttributes<HTMLElementTagNameMap["button"]> {
  /**
   * @default "button"
   */
  type?: "button" | "submit" | "reset";

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

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

---

Table of Contents

• Approach
• Usage
  • Installation
  • Set-up with Rollup
  • CLI
  • Publishing to NPM
• Available Options
• API Reference
  • @type
  • @typedef
  • @slot
  • @event
  • @restProps
  • @extends
• Contributing
• License

Approach

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

Extracted metadata:

• 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.

The generated TypeScript definitions for a component extends the SvelteComponentTyped interface available in svelte version 3.31.

Usage

Installation

Install sveld as a development dependency.

yarn add -D sveld
# OR
npm i -D sveld

Set-up with 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 with Rollup, TypeScript definitions will be written to the types folder.

The integration folder contains example set-ups:

• single-export: library that exports one component
• multi-export: multi-component library without JSDoc annotations (types are inferred)
• multi-export-typed: multi-component library with JSDoc annotations

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

Publishing to NPM

Specify the entry point for the TypeScript definitions in your package.json.

{
  "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.

Signature:

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

Example:

<script>
  /**
   * @slot {{ prop: number; doubled: number; }}
   * @slot {{ props: { class?: string; } }} description
   */

  export let prop = 0;
</script>

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

<p>
  <slot name="description" props={{ class: $$props.class }} />
</p>

@event

Use the @event tag for typing dispatched events. An event name must be specified.

Signature:

/**
 * @event {EventDetail} eventname
 */

Example:

/**
 * @event {{ key: string }} button:key
 */

export let key = "";

import { createEventDispatcher } from "svelte";

const dispatch = createEventDispatcher();

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

@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 explicitly define 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"} ButtonProps */

export const secondary = true;

import Button from "./Button.svelte";

Contributing

Refer to the contributing guidelines.

License

Apache-2.0

Changelog

0.7.1 - 2021-02-20

• only parse files with the .svelte file extension