goldmark-toc is an add-on for the goldmark Markdown parser that adds support for rendering a table-of-contents.
Demo: A web-based demonstration of the extension is available at https://abhinav.github.io/goldmark-toc/demo/.
go get go.abhg.dev/goldmark/toc@latest
To use goldmark-toc, import the toc
package.
import "go.abhg.dev/goldmark/toc"
Following that, you have three options for using this package:
- Extension: This is the easiest way to get a table of contents into your document and provides very little control over the output.
- Transformer: This is the next easiest option and provides more control over the output.
- Manual: This option requires the most work but also provides the most control.
To use this package as a simple Goldmark extension, install the Extender
when constructing the goldmark.Markdown
object.
markdown := goldmark.New(
// ...
goldmark.WithParserOptions(parser.WithAutoHeadingID()),
goldmark.WithExtensions(
// ...
&toc.Extender{},
),
)
This will add a "Table of Contents" section to the top of every Markdown document parsed by this Markdown object.
NOTE: The example above enables
parser.WithAutoHeadingID
. Without this or a custom implementation ofparser.IDs
, none of the headings in the document will have links generated for them.
If you want to use a title other than "Table of Contents",
set the Title
field of Extender
.
&toc.Extender{
Title: "Contents",
}
You can specify an ID for the title heading with the TitleID
option.
&toc.Extender{
Title: "Contents",
TitleID: "toc-header",
}
If you want the rendered HTML list to include an id,
set the ListID
field of Extender
.
&toc.Extender{
ListID: "toc",
}
This will render:
<ul id="toc">
<!-- ... -->
</ul>
By default, goldmark-toc will include all headers in the table of contents.
If you want to limit the depth of the table of contents,
use the MinDepth
and MaxDepth
field.
&toc.Extender{
MinDepth: 2,
MaxDepth: 3,
}
Headers with a level lower or higher than the specified values will not be included in the table of contents.
The Table of Contents generated by goldmark-toc matches your heading hierarchy exactly. This can be a problem if you have multiple levels of difference between items. For example, if you have the document:
# h1
### h3
goldmark-toc will generate a TOC with the equivalent of the following, resulting in an empty entry between h1 and h3.
- h1
- <blank>
- h3
You can use the Compact
option to collapse away these intermediate items.
&toc.Extender{
Compact: true,
}
With this option enabled, the hierarchy above will render as the equivalent of the following.
- h1
- h3
Installing this package as an AST Transformer provides slightly more control over the output. To use it, install the AST transformer on the Goldmark Markdown parser.
markdown := goldmark.New(...)
markdown.Parser().AddOptions(
parser.WithAutoHeadingID(),
parser.WithASTTransformers(
util.Prioritized(&toc.Transformer{
Title: "Contents",
}, 100),
),
)
This will generate a "Contents" section at the top of all Markdown documents parsed by this parser.
As with the previous example, this enables parser.WithAutoHeadingID
to get
auto-generated heading IDs.
If you use this package manually to generate Tables of Contents, you have a lot more control over the behavior. This requires a few steps.
Parse a Markdown document with goldmark.
markdown := goldmark.New(...)
markdown.Parser().AddOptions(parser.WithAutoHeadingID())
doc := markdown.Parser().Parse(text.NewReader(src))
Note that the parser must be configured to generate IDs for headers or the
headers in the table of contents won't have anything to point to. This can be
accomplished by adding the parser.WithAutoHeadingID
option as in the example
above, or with a custom implementation of goldmark/parser.IDs
by using the
snippet below.
markdown := goldmark.New(...)
pctx := parser.NewContext(parser.WithIDs(ids))
doc := parser.Parse(text.NewReader(src), parser.WithContext(pctx))
After parsing a Markdown document, inspect it with toc
.
tree, err := toc.Inspect(doc, src)
if err != nil {
// handle the error
}
If you need to limit the depth of the table of contents,
use the MinDepth
and MaxDepth
option.
tree, err := toc.Inspect(doc, src, toc.MinDepth(2), toc.MaxDepth(3))
You can render the table of contents into a Markdown list with
toc.RenderList
.
list := toc.RenderList(tree)
This builds a list representation of the table of contents to be rendered as Markdown or HTML.
You may manipulate the tree
before rendering the list.
Finally, render this table of contents along with your Markdown document:
// Render the table of contents.
if list != nil {
// list will be nil if the table of contents is empty
// because there were no headings in the document.
markdown.Renderer().Render(output, src, list)
}
// Render the document.
markdown.Renderer().Render(output, src, doc)
Alternatively, include the table of contents into your Markdown document in your desired position and render it using your Markdown renderer.
// Prepend table of contents to the front of the document.
if list != nil {
doc.InsertBefore(doc, doc.FirstChild(), list)
}
// Render the document.
markdown.Renderer().Render(output, src, doc)
If you want the rendered TOC to have an id or other attributes,
use Node.SetAttribute
on the ast.Node
returned by toc.RenderList
.
For example, with the following:
list := toc.RenderList(tree)
list.SetAttribute([]byte("id"), []byte("toc"))
The output will take the form:
<ul id="toc">
<!-- ... -->
</ul>