addRule - Turndown

Syntax

turndownService.addRule(key, rule)

Description

Adds a custom rule to the TurndownService instance. Rules define how specific HTML elements should be converted to Markdown. Each rule has a unique key and contains a filter to match elements and a replacement function to define the conversion.

Parameters

string

required

A unique identifier for the rule. Used for easy reference and debugging.

object

required

The rule object defining how to convert matching elements

Show properties

string | array | function

required

Determines which elements this rule applies to:

String: A single tag name (e.g., 'p')
Array: Multiple tag names (e.g., ['em', 'i'])
Function: Custom filter function (node, options) => boolean

function

required

Function that returns the Markdown string for the matched element.Signature: (content, node, options) => string

content: The inner content of the element (already converted)
node: The DOM node being converted
options: The TurndownService options object

function

Function to append content after the main conversion.Signature: (options) => string

Returns

TurndownService

Returns the TurndownService instance for method chaining

Examples

Strikethrough Rule

turndownService.addRule('strikethrough', {
  filter: ['del', 's', 'strike'],
  replacement: function (content) {
    return '~' + content + '~'
  }
})

Highlight Rule

turndownService.addRule('highlight', {
  filter: 'mark',
  replacement: function (content) {
    return '==' + content + '=='
  }
})

Custom Filter Function

turndownService.addRule('customLink', {
  filter: function (node, options) {
    return (
      node.nodeName === 'A' &&
      node.getAttribute('href') &&
      node.getAttribute('href').startsWith('http')
    )
  },
  replacement: function (content, node) {
    return '[' + content + '](' + node.getAttribute('href') + ')'
  }
})

Chaining Multiple Rules

turndownService
  .addRule('strikethrough', {
    filter: ['del', 's'],
    replacement: function (content) {
      return '~~' + content + '~~'
    }
  })
  .addRule('underline', {
    filter: 'u',
    replacement: function (content) {
      return '<u>' + content + '</u>'
    }
  })

Notes

Returns the instance to enable method chaining
Rules are processed in order of precedence (see Rule Precedence documentation)
Custom rules take precedence over CommonMark rules but not over the blank rule
Tag names in filters should be lowercase
The replacement function receives already-converted content for nested elements

​Syntax

​Description

​Parameters

​Returns

​Examples

​Strikethrough Rule

​Highlight Rule

​Custom Filter Function

​Chaining Multiple Rules

​Notes

Syntax

Description

Parameters

Returns

Examples

Strikethrough Rule

Highlight Rule

Custom Filter Function

Chaining Multiple Rules

Notes