Add support for prefix

Closes GH-59.
Closes GH-60.

Reviewed-by: Christian Murphy <christian.murphy.42@gmail.com>
Reviewed-by: Jonathan Haines <jonno.haines@gmail.com>

Author: wooorm

lib/contents.js

@@ -11,7 +11,7 @@ var LINK = 'link'
 var LINK_REFERENCE = 'linkReference'
 
 // Transform a list of heading objects to a markdown list.
-function contents(map, tight) {
+function contents(map, tight, prefix) {
   var minDepth = Infinity
   var index = -1
   var length = map.length
@@ -38,14 +38,14 @@ function contents(map, tight) {
   index = -1
 
   while (++index < length) {
-    insert(map[index], table, tight)
+    insert(map[index], table, tight, prefix)
   }
 
   return table
 }
 
 // Insert an entry into `parent`.
-function insert(entry, parent, tight) {
+function insert(entry, parent, tight, prefix) {
   var children = parent.children
   var length = children.length
   var last = children[length - 1]
@@ -62,30 +62,30 @@ function insert(entry, parent, tight) {
         {
           type: LINK,
           title: null,
-          url: '#' + entry.id,
+          url: '#' + (prefix || '') + entry.id,
           children: all(entry.children)
         }
       ]
     })
 
     children.push(item)
   } else if (last && last.type === LIST_ITEM) {
-    insert(entry, last, tight)
+    insert(entry, last, tight, prefix)
   } else if (last && last.type === LIST) {
     entry.depth--
 
-    insert(entry, last, tight)
+    insert(entry, last, tight, prefix)
   } else if (parent.type === LIST) {
     item = listItem()
 
-    insert(entry, item, tight)
+    insert(entry, item, tight, prefix)
 
     children.push(item)
   } else {
     item = list()
     entry.depth--
 
-    insert(entry, item, tight)
+    insert(entry, item, tight, prefix)
 
     children.push(item)
   }

lib/index.js

@@ -12,7 +12,8 @@ function toc(node, options) {
   var result = search(node, heading, settings)
   var map = result.map
 
-  result.map = map.length === 0 ? null : contents(map, settings.tight)
+  result.map =
+    map.length === 0 ? null : contents(map, settings.tight, settings.prefix)
 
   // No given heading.
   if (!heading) {

readme.md

@@ -42,14 +42,23 @@ Yields:
 
 ```javascript
 
-{ index: null,
+{
+  index: null,
   endIndex: null,
-  map:
-   { type: 'list',
-     ordered: false,
-     spread: true,
-     children:
-      [ { type: 'listItem', loose: true, spread: true, children: [Array] } ] } }
+  map: {
+    type: 'list',
+    ordered: false,
+    spread: true,
+    children: [
+      {
+        type: 'listItem',
+        loose: true,
+        spread: true,
+        children: [Array]
+      }
+    ]
+  }
+}
 ```
 
 ## API
@@ -86,6 +95,12 @@ This is inclusive, thus, when set to `3`, level three headings, are included
 
 Whether to compile list-items tightly (`boolean?`, default: `false`).
 
+###### `options.prefix`
+
+Add a prefix to links to headings (`string?`, default: `null`).
+Useful for example when later going from mdast to hast and sanitizing with
+[`hast-util-sanitize`][hast-util-sanitize].
+
 ###### `options.parents`
 
 Allows headings to be children of certain node types.
@@ -174,3 +189,5 @@ repository, organisation, or community you agree to abide by its terms.
 [contributing]: https://github.com/syntax-tree/mdast/blob/master/contributing.md
 
 [coc]: https://github.com/syntax-tree/mdast/blob/master/code-of-conduct.md
+
+[hast-util-sanitize]: https://github.com/syntax-tree/hast-util-sanitize

test/fixtures/prefix/config.json

@@ -0,0 +1,3 @@
+{
+  "prefix": "user-content-"
+}

test/fixtures/prefix/input.md

@@ -0,0 +1,9 @@
+# Something if
+
+## Something else
+
+Text.
+
+## Something elsefi
+
+# Something iffi

test/fixtures/prefix/output.json

@@ -0,0 +1,110 @@
+{
+  "index": null,
+  "endIndex": null,
+  "map": {
+    "type": "list",
+    "ordered": false,
+    "spread": true,
+    "children": [
+      {
+        "type": "listItem",
+        "loose": true,
+        "spread": true,
+        "children": [
+          {
+            "type": "paragraph",
+            "children": [
+              {
+                "type": "link",
+                "title": null,
+                "url": "#user-content-something-if",
+                "children": [
+                  {
+                    "type": "text",
+                    "value": "Something if"
+                  }
+                ]
+              }
+            ]
+          },
+          {
+            "type": "list",
+            "ordered": false,
+            "spread": false,
+            "children": [
+              {
+                "type": "listItem",
+                "loose": false,
+                "spread": false,
+                "children": [
+                  {
+                    "type": "paragraph",
+                    "children": [
+                      {
+                        "type": "link",
+                        "title": null,
+                        "url": "#user-content-something-else",
+                        "children": [
+                          {
+                            "type": "text",
+                            "value": "Something else"
+                          }
+                        ]
+                      }
+                    ]
+                  }
+                ]
+              },
+              {
+                "type": "listItem",
+                "loose": false,
+                "spread": false,
+                "children": [
+                  {
+                    "type": "paragraph",
+                    "children": [
+                      {
+                        "type": "link",
+                        "title": null,
+                        "url": "#user-content-something-elsefi",
+                        "children": [
+                          {
+                            "type": "text",
+                            "value": "Something elsefi"
+                          }
+                        ]
+                      }
+                    ]
+                  }
+                ]
+              }
+            ]
+          }
+        ]
+      },
+      {
+        "type": "listItem",
+        "loose": false,
+        "spread": false,
+        "children": [
+          {
+            "type": "paragraph",
+            "children": [
+              {
+                "type": "link",
+                "title": null,
+                "url": "#user-content-something-iffi",
+                "children": [
+                  {
+                    "type": "text",
+                    "value": "Something iffi"
+                  }
+                ]
+              }
+            ]
+          }
+        ]
+      }
+    ]
+  }
+}