Merge pull request #527 from outline/stable-headings

Stable heading IDs

app/components/Editor/components/Contents.js

@@ -64,6 +64,8 @@ class Contents extends Component {
   }
 
   render() {
+    const { editor } = this.props;
+
     // If there are one or less headings in the document no need for a minimap
     if (this.headings.size <= 1) return null;
 
@@ -71,7 +73,7 @@ class Contents extends Component {
       <Wrapper>
         <Sections>
           {this.headings.map(heading => {
-            const slug = headingToSlug(heading);
+            const slug = headingToSlug(editor.value.document, heading);
             const active = this.activeHeading === slug;
 
             return (

app/components/Editor/components/Heading.js

@@ -27,7 +27,7 @@ function Heading(props: Props) {
   const parentIsDocument = parent instanceof Document;
   const firstHeading = parentIsDocument && parent.nodes.first() === node;
   const showPlaceholder = placeholder && firstHeading && !node.text;
-  const slugish = headingToSlug(node);
+  const slugish = headingToSlug(editor.value.document, node);
   const showHash = readOnly && !!slugish;
   const Component = component;
   const emoji = editor.props.emoji || '';

app/components/Editor/headingToSlug.js

@@ -1,9 +1,25 @@
 // @flow
 import { escape } from 'lodash';
-import { Node } from 'slate';
+import { Document, Block, Node } from 'slate';
 import slug from 'slug';
 
-export default function headingToSlug(node: Node) {
-  const level = node.type.replace('heading', 'h');
-  return escape(`${level}-${slug(node.text)}-${node.key}`);
+// finds the index of this heading in the document compared to other headings
+// with the same slugified text
+function indexOfType(document, heading) {
+  const slugified = escape(slug(heading.text));
+  const headings = document.nodes.filter((node: Block) => {
+    if (!node.text) return false;
+    return node.type.match(/^heading/) && slugified === escape(slug(node.text));
+  });
+
+  return headings.indexOf(heading);
+}
+
+// calculates a unique slug for this heading based on it's text and position
+// in the document that is as stable as possible
+export default function headingToSlug(document: Document, node: Node) {
+  const slugified = escape(slug(node.text));
+  const index = indexOfType(document, node);
+  if (index === 0) return slugified;
+  return `${slugified}-${index}`;
 }