ByteMD

ByteMD is a Markdown editor component built with Svelte. It could also be used in other libraries/frameworks such as React, Vue and Angular.

Playground here: https://bytemd.js.org/playground/

Features

1. Lightweight and framework agnostic: ByteMD is built with Svelte. It compiles to vanilla JS DOM manipulation without importing any UI Framework runtime bundle, which makes it lightweight, and easily adapted to other libraries/frameworks.
2. Easy to extend: ByteMD has a plugin system to extend the basic Markdown syntax, which makes it easy to add additional features such as code syntax highlight, math equation and Mermaid flowcharts. You can also write your own plugin if these ones don't meet your needs.
3. Secure by default: Cross-site scripting(XSS) attack such as <script> and <img onerror> have been correctly handled by ByteMD. No need to introduce extra DOM sanitize steps.
4. SSR compatible: ByteMD could be used in the Server-side rendering(SSR) environment without extra config. SSR is widely used in some cases due to its better SEO and fast time-to-content in slow network connection.

Installation

Package	Status	Description
bytemd		Svelte/Vanilla JS component
@bytemd/react		React component
@bytemd/vue		Vue 2 component
@bytemd/vue-next		Vue 3 component

Legacy browsers support

The default entry of NPM package only supports modern browsers. To make legacy browsers (IE9+) work, You can compile it with ESNext -> ES5 transpilers, such as Babel or SWC.

The ES5 bundle will no longer be available after version 1.11.0. If you need it, you can use version 1.11.0 or earlier versions

Notice that polyfills are not included, and should be imported manually, see the legacy browser example.

Usage

There are two components: Editor and Viewer. Editor is the Markdown editor, as the name suggests; Viewer is commonly used to display rendered Markdown results without editing.

Before using the component, remember to import CSS file to make styles correct:

import 'bytemd/dist/index.css'

Svelte

<script>
  import { Editor, Viewer } from 'bytemd'
  import gfm from '@bytemd/plugin-gfm'

  let value
  const plugins = [
    gfm(),
    // Add more plugins here
  ]

  function handleChange(e) {
    value = e.detail.value
  }
</script>

<template>
  <Editor {value} {plugins} on:change={handleChange} />
</template>

React

import gfm from '@bytemd/plugin-gfm'
import { Editor, Viewer } from '@bytemd/react'

const plugins = [
  gfm(),
  // Add more plugins here
]

const App = () => {
  const [value, setValue] = useState('')

  return (
    <Editor
      value={value}
      plugins={plugins}
      onChange={(v) => {
        setValue(v)
      }}
    />
  )
}

Vue

<template>
  <Editor :value="value" :plugins="plugins" @change="handleChange" />
</template>

<script>
import gfm from '@bytemd/plugin-gfm'
import { Editor, Viewer } from '@bytemd/vue'

const plugins = [
  gfm(),
  // Add more plugins here
]

export default {
  components: { Editor },
  data() {
    return { value: '', plugins }
  },
  methods: {
    handleChange(v) {
      this.value = v
    },
  },
}
</script>

Vanilla JS

import gfm from '@bytemd/plugin-gfm'
import { Editor, Viewer } from 'bytemd'

const plugins = [
  gfm(),
  // Add more plugins here
]

const editor = new Editor({
  target: document.body, // DOM to render
  props: {
    value: '',
    plugins,
  },
})

editor.$on('change', (e) => {
  editor.$set({ value: e.detail.value })
})

Options

Viewer

Key	Type	Description
value	string (required)	Markdown text
plugins	BytemdPlugin[]	ByteMD plugin list
sanitize	(schema: Schema) => Schema	Sanitize strategy
remarkRehype	documentation	remark-rehype config options

Editor

Editor component also accepts the options of Viewer for preview. Besides that, there are some other options:

Key	Type	Description
mode	split, tab, auto	Editor display mode, default: auto
previewDebounce	number	Debounce time (ms) for preview, default: 300
placeholder	string	Editor placeholder
editorConfig	documentation	CodeMirror editor config
locale		i18n locale. Available locales could be found at bytemd/locales, default: use en.json
uploadImages	function	Specify how to upload images. If set, the image icon will appear on the toolbar
maxLength	number	Maximum length (number of characters) of value

Style customization

Editor

The default height of ByteMD Editor is 300px. It could be overridden by CSS:

.bytemd {
  height: calc(100vh - 200px);
}

The other styles could also be overridden, see the default style.

Viewer

There is no built-in styles for the Viewer. You could use third-party markdown themes, for example juejin-markdown-themes and github-markdown-css.

Plugin System

ByteMD provides a powerful plugin system for customization. There are several official plugins to support features such as code syntax highlight, math equation and Mermaid flowcharts.

If you have more customized needs, you could also write your own plugin to support them.

Official Plugins

Package	Status	Description
@bytemd/plugin-breaks		Support breaks
@bytemd/plugin-frontmatter		Parse frontmatter
@bytemd/plugin-gemoji		Support Gemoji shortcodes
@bytemd/plugin-gfm		Support GFM (autolink literals, strikethrough, tables, tasklists)
@bytemd/plugin-highlight		Highlight code blocks
@bytemd/plugin-highlight-ssr		Highlight code blocks (SSR compatible)
@bytemd/plugin-math		Support math formula
@bytemd/plugin-math-ssr		Support math formula (SSR compatible)
@bytemd/plugin-medium-zoom		Zoom images like Medium
@bytemd/plugin-mermaid		Support Mermaid diagram

Technical Overview

ByteMD uses remark and rehype ecosystem to process Markdown. The complete process is as follows:

1. The markdown text is parsed to an AST
2. The Markdown AST could be manipulated by several remark plugins
3. The Markdown AST is transformed to a HTML AST
4. The HTML AST is sanitized for security reason
5. The HTML AST could be manipulated by several rehype plugins
6. The HTML AST is stringified to HTML
7. Some extra DOM manipulation after the HTML being rendered

It could also be described as a flowchart:

The 2,5,7 steps are designed for user customization via ByteMD plugin API.

Authoring a Plugin

We'll take Math formula plugin as an example to walk you through the process.

First of all, scaffold the project according to the BytemdPlugin type signature:

import type { BytemdPlugin } from 'bytemd'

export default function mathPlugin(): BytemdPlugin {
  return {
    // to be implement
  }
}

Then we look into the requirement more closely: If we want to render syntax like $a+b$ to Math formula, there are several things we need to do:

• Support $a+b$ syntax as a Math formula in Markdown (step 2)
• Render these nodes correctly in HTML (step 5 or 7)
• Additionally, an extra icon in the toolbar would be great for user convenience

For the first thing, luckily, we don't need to implement it with our own because remark-math already did it. The only thing we need to do is to import and use it:

import type { BytemdPlugin } from 'bytemd'
+import remarkMath from 'remark-math'

export default function mathPlugin(): BytemdPlugin {
  return {
-    // to be implement
+    remark: (processor) => processor.use(remarkMath),
  }
}

Then consider the second thing, it would be a little complicated because we have two choices, do it in step 5 or 7. The difference is that step 5 is more friendly with SSR, while step 7 hand over the rendering to the client-side. This is why we have two plugin: @bytemd/plugin-math and @bytemd/plugin-math-ssr.

// if we choose step 5:
import type { BytemdPlugin } from 'bytemd'
import remarkMath from 'remark-math'
+import rehypeKatex from 'rehype-katex'

export default function mathPlugin(): BytemdPlugin {
  return {
    remark: (processor) => processor.use(remarkMath),
+   rehype: (processor) => processor.use(rehypeKatex),
  }
}

// if we choose step 7:
import type { BytemdPlugin } from 'bytemd'
import remarkMath from 'remark-math'
+import rehypeKatex from 'rehype-katex'

export default function mathPlugin(): BytemdPlugin {
  return {
    remark: (processor) => processor.use(remarkMath),
+   viewerEffect({ markdownBody }) {
+     const renderMath = async (selector: string, displayMode: boolean) => {
+       const katex = await import('katex').then((m) => m.default)
+
+       const els = markdownBody.querySelectorAll<HTMLElement>(selector)
+       els.forEach((el) => {
+         katex.render(el.innerText, el, { displayMode })
+       })
+     }
+
+     renderMath('.math.math-inline', false)
+     renderMath('.math.math-display', true)
+   },
  }
}

The last thing is to add an icon to the toolbar. we use the actions prop to implement it:

export default function mathPlugin(): BytemdPlugin {
  return {
    actions: [
      {
        title: 'Insert an math formula',
        icon: '', // 16x16 SVG icon
        handler: {
          type: 'action',
          click(ctx) {
            // to be implement:
            // the `ctx` is an instance of `BytemdEditorContext`, which has
            // several utility methods to help operate the CodeMirror editor state.

            // remember to call `focus` to avoid lost of focus
            editor.focus()
          },
        },
      },
    ],
  }
}

Now we have completed a minimalist version of the plugin! For more details and references please check out the source code.

Contributors

License

MIT