Fix for issue #380 Custom attributes for toolbar buttons

Added "attributes" option to custom toolbar button

README.md

@@ -377,6 +377,10 @@ const easyMDE = new EasyMDE({
             },
             className: "fa fa-star",
             title: "Custom Button",
+            attributes: { // for custom attributes
+                id: "custom-id",
+                "data-value": "custom value" // HTML5 data-* attributes need to be enclosed in quotation marks ("") because of the dash (-) in its name.
+            }
         },
         "|" // Separator
         // [, ...]

src/js/easymde.js

@@ -231,6 +231,12 @@ function createToolbarButton(options, enableActions, enableTooltips, shortcuts,
         }
     }
 
+    if (options.attributes) {
+        for (var attribute in options.attributes) {
+            el.setAttribute(attribute, options.attributes[attribute]);
+        }
+    }
+
     if (options.noDisable) {
         el.classList.add('no-disable');
     }