VSC Quill Delta to HTML Converter

Converts Quill's Delta format to HTML (insert ops only) with properly nested lists. It has full support for Quill operations - including images, videos, formulas, tables, and mentions. Conversion can be performed in vanilla Dart (i.e., server-side or CLI) or in Flutter.

This is a complete port of the popular quill-delta-to-html Typescript/Javascript package to Dart.

This converter can convert to HTML for a number of purposes, not the least of which is for generating HTML-based emails. It makes a great pairing with Flutter Quill.

You can try a live demo of the conversion by running the example Flutter app.

Quickstart

To get started, add this package to your pubspec.yaml dependencies.

Usage

import 'package:vsc_quill_delta_to_html/vsc_quill_delta_to_html.dart';

void main() {
  final deltaOps = [
    {'insert': 'Hello\n'},
    {
      'insert': 'This is colorful',
      'attributes': {'color': '#f00'}
    }
  ];

  final converter = QuillDeltaToHtmlConverter(
    ops,
    ConverterOptions.forEmail(),
  );

  final html = converter.convert();
  print(html);
}

Configuration

QuillDeltaToHtmlConverter accepts a few configuration (ConverterOptions, OpConverterOptions, and OpAttributeSanitizerOptions) options as shown below:

Option	Type	Default	Description
converterOptions.paragraphTag	string	'p'	Custom tag to wrap inline html elements
converterOptions.encodeHtml	boolean	true	If true, <, >, /, ', ", & characters in content will be encoded.
converterOptions.classPrefix	string	'ql'	A css class name to prefix class generating styles such as size, font, etc.
converterOptions.inlineStylesFlag	boolean	false	If true, use inline styles instead of classes.
converterOptions.inlineStyles	InlineStyles	null	If non-null, use inline styles instead of classes. See Rendering Inline Styles section below for usage.
multiLineBlockquote	boolean	true	Instead of rendering multiple blockquote elements for quotes that are consecutive and have same styles(align, indent, and direction), it renders them into only one
multiLineHeader	boolean	true	Same deal as multiLineBlockquote for headers
multiLineCodeblock	boolean	true	Same deal as multiLineBlockquote for code-blocks
multiLineParagraph	boolean	true	Set to false to generate a new paragraph tag after each enter press (new line)
multiLineCustomBlock	boolean	true	Same deal as multiLineBlockquote for custom blocks.
bulletListTag	string	'ul'	Tag for unordered bullet lists.
orderedListTag	string	'ol'	Tag for ordered/numbered lists.
converterOptions.linkRel	string	none generated	Specifies a value to put on the rel attr on all links. This can be overridden by an individual link op by specifying the rel attribute in the respective op's attributes
converterOptions.linkTarget	string	'_blank'	Specifies target for all links; use '' (empty string) to not generate target attribute. This can be overridden by an individual link op by specifiying the target with a value in the respective op's attributes.
converterOptions.allowBackgroundClasses	boolean	false	If true, css classes will be added for background attr
sanitizerOptions.urlSanitizer	String? Function(String url)	null	A function that is called once per url in the ops (image, video, link) for you to do custom sanitization. If your function returns a string, it is assumed that you sanitized the url and no further sanitization will be done by the library; when anything other than a string is returned (e.g. undefined), it is assumed that no sanitization has been done and the library's own function will be used to clean up the url
sanitizerOptions.allow8DigitHexColors	boolean	false	If true, hex colors in #AARRGGBB format are allowed in the ops
converterOptions.customTag	String? Function(String format, DeltaInsertOp op)	null	Callback allows to provide custom html tag for some format
converterOptions.customTagAttributes	Map<String, String>? Function(DeltaInsertOp op)	null	Allows custom html tag attributes for the given op
converterOptions.customCssClasses	List<String>? Function(DeltaInsertOp op)	null	Allows custom CSS classes for the given op
converterOptions.customCssStyles	List<String>? Function(DeltaInsertOp op)	null	Allows custom CSS styles attributes for the given op

Rendering Quill Formats

You can customize the rendering of Quill formats by registering render callbacks before calling the convert() method.

There is a beforeRender and an afterRender callback. They are called multiple times before and after rendering each group. A group is one of:

• continuous sets of inline elements
• a video element
• list elements
• block elements (header, code-block, blockquote, align, indent, and direction)

beforeRender event is called with raw operation objects for you to generate and return your own html. If you return null, the system will return its own generated html.

afterRender event is called with generated html for you to inspect, maybe make some changes, and return your modified or original html.

converter.beforeRender = (GroupType groupType, TDataGroup data) {
    // ... generate your own html 
    // return your html
};

converter.afterRender = (GroupType groupType, String htmlString) {
    // modify if you wish
    // return the html
};

html = converter.convert();

Following shows the parameter formats for beforeRender event:

groupType	data
video	VideoItem
block	BlockGroup
list	ListGroup
inline-group	InlineGroup

Rendering Inline Styles

If you are rendering to HTML that you intend to include in an email, using classes and a style sheet are not recommended, as not all browsers support style sheets. vsc_quill_delta_to_html supports rendering inline styles instead. The easiest way to enable this is to pass the option inlineStylesFlag: true.

You can customize styles by passing an object to inlineStyles instead:

inlineStyles: InlineStyles({
  'font': InlineStyleType(
      fn: (value, _) => defaultInlineFonts[value] ?? 'font-family:$value'),
  'size': InlineStyleType(map: {
    'small': 'font-size: 0.75em',
    'large': 'font-size: 1.5em',
    'huge': 'font-size: 2.5em',
  }),
  'indent': InlineStyleType(fn: (value, op) {
    final indentSize = (double.tryParse(value) ?? double.nan) * 3;
    final side = op.attributes['direction'] == 'rtl' ? 'right' : 'left';
    return 'padding-$side:${indentSize}em';
  }),
  'direction': InlineStyleType(fn: (value, op) {
    if (value == 'rtl') {
      final textAlign =
      isTruthy(op.attributes['align']) ? '' : '; text-align:inherit';
      return ('direction:rtl$textAlign');
    } else {
      return null;
    }
  }),
  'list': InlineStyleType(map: {
    'checked': "list-style-type:'\\2611';padding-left: 0.5em;",
    'unchecked': "list-style-type:'\\2610';padding-left: 0.5em;",
  }),
});

Keys to this object are the names of attributes from Quill. The values are either a simple lookup table (like in the list example above) used to map values to styles, or a fn(value, op) which returns a style string.

Rendering Custom Blot Formats

You need to tell system how to render your custom blot by registering a renderer callback function to renderCustomWith method before calling the convert() method.

If you would like your custom blot to be rendered as a block (not inside another block or grouped as part of inlines), then add renderAsBlock: true to its attributes.

Example:

final ops = [
    {insert: {'my-blot': {id: 2, text: 'xyz'}}, attributes: {renderAsBlock: true|false}}
];

let converter = new QuillDeltaToHtmlConverter(ops);

// customOp is your custom blot op
// contextOp is the block op that wraps this op, if any. 
// If, for example, your custom blot is located inside a list item,
// then contextOp would provide that op. 
converter.renderCustomWith = (DeltaInsertOp customOp, DeltaInsertOp? contextOp) {
    if (customOp.insert.type == 'my-blot') {
        return '<span>Some custom blot</span>';
    } else {
        return 'Unmanaged custom blot!';
    }
});

html = converter.convert();

customOp object will have the following format:

{
    insert: {
        type: string //whatever you specified as key for insert, in above example: 'my-blot'
        value: any // value for the custom blot  
    }, 
    attributes: {
        // ... any attributes custom blot may have
    }
}

Advanced Custom Rendering Using Grouped Ops

If you want to do the full rendering yourself, you can do so by getting the processed & grouped ops.

final groupedOps = converter.getGroupedOps();

Each element in groupedOps array will be an instance of the following types: InlineGroup, VideoItem, BlockGroup, ListGroup, ListItem, BlotBlock.

BlotBlock represents custom blots with renderAsBlock:true property pair in its attributes