Support individual header level selection.

Closes valeriangalliat#27.

Author: valeriangalliat

CHANGELOG.md

@@ -6,6 +6,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 * Drop Babel. This drops support for Node.js versions that doesn't
   support ES6.
 * Support code in titles. ([#27])
+* Support individual header level selection. ([#27])
 
 ## [3.0.0] - 2017-02-06
 * Use existing ID as slug if present. This drops the support for

README.md

@@ -16,17 +16,17 @@ See a [demo as JSFiddle](https://jsfiddle.net/9ukc8dy6/).
 
 The `opts` object can contain:
 
-Name              | Description                                   | Default
-------------------|-----------------------------------------------|------------------------------------
-`level`           | Minimum level to apply anchors on.            | 1
-`slugify`         | A custom slugification function.              | [string.js' `slugify`][slugify]
-`permalink`       | Whether to add permalinks next to titles.     | `false`
-`renderPermalink` | A custom permalink rendering function.        | See [`index.es6.js`](index.es6.js)
-`permalinkClass`  | The class of the permalink anchor.            | `header-anchor`
-`permalinkSymbol` | The symbol in the permalink anchor.           | `¶`
-`permalinkBefore` | Place the permalink before the title.         | `false`
-`permalinkHref`   | A custom permalink `href` rendering function. | See [`index.es6.js`](index.es6.js)
-`callback`        | Called with token and info after rendering.   | `undefined`
+Name              | Description                                                    | Default
+------------------|----------------------------------------------------------------|-----------------------------------
+`level`           | Minimum level to apply anchors on or array of selected levels. | 1
+`slugify`         | A custom slugification function.                               | [string.js' `slugify`][slugify]
+`permalink`       | Whether to add permalinks next to titles.                      | `false`
+`renderPermalink` | A custom permalink rendering function.                         | See [`index.es6.js`](index.es6.js)
+`permalinkClass`  | The class of the permalink anchor.                             | `header-anchor`
+`permalinkSymbol` | The symbol in the permalink anchor.                            | `¶`
+`permalinkBefore` | Place the permalink before the title.                          | `false`
+`permalinkHref`   | A custom permalink `href` rendering function.                  | See [`index.es6.js`](index.es6.js)
+`callback`        | Called with token and info after rendering.                    | `undefined`
 
 [slugify]: http://stringjs.com/#methods/slugify
 
@@ -35,8 +35,12 @@ the above options, and then all the usual markdown-it rendering
 arguments.
 
 All headers above `level` will then have an `id` attribute with a slug
-of their content, and if `permalink` is `true`, a `¶` symbol linking to
-the header itself.
+of their content. `level` can also be an array of headers levels to
+apply the anchor, like `[2, 3]` to have an anchor on only level 2 and
+3 headers.
+
+If `permalink` is `true`, a `¶` symbol linking to the header itself will
+be added.
 
 You may want to use the [link symbol](http://graphemica.com/🔗) as
 `permalinkSymbol`, or a symbol from your favorite web font.

index.js

@@ -47,16 +47,23 @@ const uniqueSlug = (slug, slugs) => {
   return slug + '-' + slugs[slug]
 }
 
+const isLevelSelectedNumber = selection => level => level >= selection
+const isLevelSelectedArray = selection => level => selection.includes(level)
+
 const anchor = (md, opts) => {
   opts = Object.assign({}, anchor.defaults, opts)
 
   md.core.ruler.push('anchor', state => {
     const slugs = {}
     const tokens = state.tokens
 
+    const isLevelSelected = Array.isArray(opts.level)
+      ? isLevelSelectedArray(opts.level)
+      : isLevelSelectedNumber(opts.level)
+
     tokens
       .filter(token => token.type === 'heading_open')
-      .filter(token => token.tag.substr(1) >= opts.level)
+      .filter(token => isLevelSelected(Number(token.tag.substr(1))))
       .forEach(token => {
         // Aggregate the next token children text.
         const title = tokens[tokens.indexOf(token) + 1].children

test.js

@@ -18,6 +18,11 @@ equal(
   '<h1>H1</h1>\n<h2 id="h2">H2</h2>\n'
 )
 
+equal(
+  md().use(anchor, { level: [2, 4] }).render('# H1\n\n## H2\n\n### H3\n\n#### H4\n\n##### H5'),
+  '<h1>H1</h1>\n<h2 id="h2">H2</h2>\n<h3>H3</h3>\n<h4 id="h4">H4</h4>\n<h5>H5</h5>\n'
+)
+
 equal(
   md().use(anchor, { permalink: true }).render('# H1'),
   '<h1 id="h1">H1 <a class="header-anchor" href="#h1" aria-hidden="true">¶</a></h1>\n'