Allow to generate lower case header references through the config

This makes the references consistent/compatible with GitHub,
GitLab, Pandoc and many other tools.

This behavior can be enabled in config.json with:

```
"linkifyHeaderStyle": "gfm"
```

Signed-off-by: hoijui <hoijui.quaero@gmail.com>

5 files changed, 13 insertions, 4 deletions

diff --git a/config.json.example b/config.json.example
index f627fadb..e3bd54b4 100644
--- a/config.json.example
+++ b/config.json.example
@@ -123,6 +123,7 @@
         {
           "connectionString": "change this",
           "container": "change this"
-        }
+        },
+        "linkifyHeaderStyle": "gfm"
     }
 }
diff --git a/lib/config/default.js b/lib/config/default.js
index 19bbeb21..f5cceac6 100644
--- a/lib/config/default.js
+++ b/lib/config/default.js
@@ -157,5 +157,6 @@ module.exports = {
   allowEmailRegister: true,
   allowGravatar: true,
   allowPDFExport: true,
-  openID: false
+  openID: false,
+  linkifyHeaderStyle: 'keep-case'
 }
diff --git a/lib/web/statusRouter.js b/lib/web/statusRouter.js
index da69e62c..1d9a1157 100644
--- a/lib/web/statusRouter.js
+++ b/lib/web/statusRouter.js
@@ -96,7 +96,8 @@ statusRouter.get('/config', function (req, res) {
     debug: config.debug,
     version: config.fullversion,
     DROPBOX_APP_KEY: config.dropbox.appKey,
-    allowedUploadMimeTypes: config.allowedUploadMimeTypes
+    allowedUploadMimeTypes: config.allowedUploadMimeTypes,
+    linkifyHeaderStyle: config.linkifyHeaderStyle
   }
   res.set({
     'Cache-Control': 'private', // only cache by client
diff --git a/public/js/extra.js b/public/js/extra.js
index 91984c2c..d381576f 100644
--- a/public/js/extra.js
+++ b/public/js/extra.js
@@ -833,7 +833,11 @@ const linkifyAnchors = (level, containingElement) => {
     if (header.getElementsByClassName('anchor').length === 0) {
       if (typeof header.id === 'undefined' || header.id === '') {
         // to escape characters not allow in css and humanize
-        const id = slugifyWithUTF8(getHeaderContent(header))
+        let id = slugifyWithUTF8(getHeaderContent(header))
+        // to make compatible with GitHub, GitLab, Pandoc and many more
+        if (window.linkifyHeaderStyle !== 'keep-case') {
+          id = id.toLowerCase()
+        }
         header.id = id
       }
       if (!(typeof header.id === 'undefined' || header.id === '')) {
diff --git a/public/js/lib/common/constant.ejs b/public/js/lib/common/constant.ejs
index a94b815e..bbcb8c7a 100644
--- a/public/js/lib/common/constant.ejs
+++ b/public/js/lib/common/constant.ejs
@@ -5,4 +5,6 @@ window.version = '<%- version %>'
 
 window.allowedUploadMimeTypes = <%- JSON.stringify(allowedUploadMimeTypes) %>
 
+window.linkifyHeaderStyle = <%- JSON.stringify(linkifyHeaderStyle) %>
+
 window.DROPBOX_APP_KEY = '<%- DROPBOX_APP_KEY %>'