uiwjs/react-md-editor v3.16.0

on GitHub

const title2 = {
  name: 'title3',
  keyCommand: 'title3',
+  render: (command, disabled, executeCommand) => {
+    return (
+      <button 
+        aria-label="Insert title3"
+        disabled={disabled}
+        onClick={(evn) => {
+          evn.stopPropagation();
+          executeCommand(command, command.groupName)
+        }}
+      >
+        btn
+      </button>
+    )
+  },
  execute: (state, api) => {
    let modifyText = `## ${state.selectedText}\n`;
    if (!state.selectedText) {
      modifyText = `## `;
    }
    api.replaceSelection(modifyText);
  },
}