HTML Parser

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Editing

HTML

By default, when you paste content into the Slate editor, it will utilize the clipboard's 'text/plain'data. While this is suitable for certain scenarios, there are times when you want users to be able to paste content while preserving its formatting. To achieve this, your editor should be capable of handling 'text/html'data.

To experience the seamless preservation of formatting, simply copy and paste rendered HTML rich text content (not the source code) from another website into this editor. You'll notice that the formatting of the pasted content is maintained.

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HTML -> Slate

Here's a comprehensive list of plugins that support HTML deserialization, along with their corresponding HTML elements and styles:

Plugin Deserialization Rules

Text Formatting

• BoldPlugin: <strong>, <b>, or style="font-weight: 600|700|bold"
• ItalicPlugin: <em>, <i>, or style="font-style: italic"
• UnderlinePlugin: <u> or style="text-decoration: underline"
• StrikethroughPlugin: <s>, <del>, <strike>, or style="text-decoration: line-through"
• SubscriptPlugin: <sub> or style="vertical-align: sub"
• SuperscriptPlugin: <sup> or style="vertical-align: super"
• CodePlugin: <code> or style="font-family: Consolas" (not within a <pre> tag)
• KbdPlugin: <kbd>

Paragraphs and Headings

• ParagraphPlugin: <p>
• HeadingPlugin: <h1>, <h2>, <h3>, <h4>, <h5>, <h6>

Lists

• ListPlugin:
  • Unordered List: <ul>
  • Ordered List: <ol>
  • List Item: <li>
• IndentListPlugin:
  • List Item: <li>
  • Parses aria-level attribute for indentation

Blocks

• BlockquotePlugin: <blockquote>
• CodeBlockPlugin:
  • Deserializes <pre> elements
  • Deserializes <p> elements with fontFamily: 'Consolas' style
  • Splits content into code lines
  • Preserves language information if available
• HorizontalRulePlugin: <hr>

Links and Media

• LinkPlugin: <a>
• ImagePlugin: <img>
• MediaEmbedPlugin: <iframe>

Tables

• TablePlugin:
  • Table: <table>
  • Table Row: <tr>
  • Table Cell: <td>
  • Table Header Cell: <th>

Text Styling

• FontBackgroundColorPlugin: style="background-color: *"
• FontColorPlugin: style="color: *"
• FontFamilyPlugin: style="font-family: *"
• FontSizePlugin: style="font-size: *"
• FontWeightPlugin: style="font-weight: *"
• HighlightPlugin: <mark>

Layout and Formatting

• AlignPlugin: style="text-align: *"
• LineHeightPlugin: style="line-height: *"

Deserialization Properties

Plugins can define various properties to control HTML deserialization:

• parse: A function to parse an HTML element into a Plate node
• query: A function that determines if the deserializer should be applied
• rules: An array of rule objects that define valid HTML elements and attributes
• isElement: Indicates if the plugin deserializes elements
• isLeaf: Indicates if the plugin deserializes leaf nodes
• attributeNames: List of HTML attribute names to store in node.attributes
• withoutChildren: Excludes child nodes from deserialization
• rules: Array of rule objects for element matching
  • validAttribute: Valid element attributes
  • validClassName: Valid CSS class name
  • validNodeName: Valid HTML tag names
  • validStyle: Valid CSS styles

Extending Deserialization

You can extend or customize the deserialization behavior of any plugin. Here's an example of how you might extend the CodeBlockPlugin:

import { CodeBlockPlugin } from '@udecode/plate-code-block';
 
const CustomCodeBlockPlugin = CodeBlockPlugin.extend({
  parsers: {
    html: {
      deserializer: {
        parse: ({ element }) => {
          const language = element.getAttribute('data-language');
          const textContent = element.textContent || '';
          const lines = textContent.split('\n');
          
          return {
            type: CodeBlockPlugin.key,
            language,
            children: lines.map((line) => ({
              type: CodeLinePlugin.key,
              children: [{ text: line }],
            })),
          };
        },
        rules: [
          ...CodeBlockPlugin.parsers.html.deserializer.rules,
          { validAttribute: 'data-language' },
        ],
      },
    },
  },
});

This customization adds support for a data-language attribute in code block deserialization and preserves the language information.

Advanced Deserialization Example

The IndentListPlugin provides a more complex deserialization process:

1. It transforms HTML list structures into indented paragraphs.
2. It handles nested lists by preserving the indentation level.
3. It uses the aria-level attribute to determine the indentation level.

Here's a simplified version of its deserialization logic:

export const IndentListPlugin = createTSlatePlugin<IndentListConfig>({
  // ... other configurations ...
  parsers: {
    html: {
      deserializer: {
        isElement: true,
        parse: ({ editor, element, getOptions }) => ({
          indent: Number(element.getAttribute('aria-level')),
          listStyleType: element.style.listStyleType,
          type: editor.getType(ParagraphPlugin),
        }),
        rules: [
          {
            validNodeName: 'LI',
          },
        ],
      },
    },
  },
});

Slate -> React -> HTML

Installation

npm install @udecode/plate-html

Usage

// ...
import { HtmlReactPlugin } from '@udecode/plate-html/react';
import { DndProvider } from 'react-dnd';
import { HTML5Backend } from 'react-dnd-html5-backend';
 
const editor = createPlateEditor({ 
  plugins: [
    HtmlReactPlugin
    // all plugins that you want to serialize
  ],
  override: {
    // do not forget to add your custom components, otherwise it won't work
    components: createPlateUI(),
  },
});
 
const html = editor.api.htmlReact.serialize({
  nodes: editor.children,
  // if you use @udecode/plate-dnd
  dndWrapper: (props) => <DndProvider backend={HTML5Backend} {...props} />,
});

API

editor.api.htmlReact.serialize

Convert Slate Nodes into HTML string.