Changed the behavior of `timestampTag` to fallback on the built-in rules when the function does not return a boolean. See #856.

HISTORY.md

@@ -3,10 +3,12 @@
 https://github.com/josdejong/jsoneditor
 
 
-## 2019-12-11, version 7.6.0
+## 2019-12-11, version 8.0.0
 
 - Implemented option `timestampFormat` which allows customizing the formatting
   of timestamp tags. See also option `timestampTag`. Thanks @smallp.
+- Changed the behavior of `timestampTag` to fallback on the built-in rules when
+  the function does not return a boolean. See #856.  
 - Reverted the heuristics introduced in `v7.3.0` to check whether some field
   contains a timestamp based on the field name, because they can give wrong 
   timestamps in case of values in seconds instead of the assumed milliseconds 

docs/api.md

@@ -476,8 +476,12 @@ Constructs a new JSONEditor.
   than Jan 1th 2000, `946684800000`.
   
   When `timestampTag` a is a function, a timestamp tag will be displayed when 
-  this function returns `true`. The function is invoked with an object as first 
-  parameter:
+  this function returns `true`, and no timestamp is displayed when the function
+  returns `false`. When the function returns a non-boolean value like `null`
+  or `undefined`, JSONEditor will fallback on the built-in rules to determine
+  whether or not to show a timestamp.   
+  
+  The function is invoked with an object as first parameter:
   
   ```
   {

src/js/Node.js

@@ -1961,18 +1961,22 @@ export class Node {
 
     const timestampTag = this.editor.options.timestampTag
     if (typeof timestampTag === 'function') {
-      return timestampTag({
+      const result = timestampTag({
         field: this.field,
         value: this.value,
         path: this.getPath()
       })
-    }
 
-    if (timestampTag === true) {
+      if (typeof result === 'boolean') {
+        return result
+      } else {
+        return isTimestamp(this.field, this.value)
+      }
+    } else if (timestampTag === true) {
       return isTimestamp(this.field, this.value)
+    } else {
+      return false
     }
-
-    return false
   }
 
   /**