I just bumped decap-cms-app @ 3.5.0 (from 3.4.0).

After the esm fixes, there are a few lingering things that prevent it from fully functioning.

Note: with the below fixes / workarounds, I have decap-cms-app working in Next.js with React 19.

1. can't resolve 'slate-hyperscript'

decap-cms-app does not declare a dependency / peerDependency on slate-hyperscript, so it fails to resolve (nested dependency from decap-cms-core).

Error

Module not found: Can't resolve 'slate-hyperscript'
   5 | });
   6 | exports.default = void 0;
>  7 | var _slateHyperscript = require("slate-hyperscript");

Workaround

npm i slate-hyperscript

Proposed Fix

Adding slate-hyperscript to decap-cms-app/package.json#peerDependencies should probably work, but peerDeps are notoriously problematic.

2. clean-stack@4.x is not browser friendly

clean-stack@4.x imports os, which is a node module (node:os), and not resolved in browser-land. This was fixed and released in clean-stack@5.0.0.

Error

os is not defined
ReferenceError: os is not defined at [project]/node_modules/decap-cms-app/node_modules/clean-stack/index.js

Workaround

add a local override to bump clean-stack@5.2.0 to your package.json:

  "overrides": {
    "clean-stack": "5.2.0"
  }

Proposed Fix

bump clean-stack@^5.2.0 in decap-cms-core

3. Next.js app fails to resolve css

• ol/ol.css
• codemirror/lib/codemirror.css
• codemirror/theme/material.css

Error (with turbopack)

Module [project]/node_modules/ol/ol.css [client] (css) was instantiated because it was required from module [project]/node_modules/decap-cms-widget-map/dist/esm/withMapControl.js [client] (ecmascript), but the module factory is not available. It might have been deleted in an HMR update.

Error (without turbopack):

./node_modules/codemirror/lib/codemirror.css
Global CSS cannot be imported from within node_modules.
Read more: https://nextjs.org/docs/messages/css-npm
Location: node_modules/decap-cms-widget-code/dist/esm/CodeControl.js

Workaround

patch-package and remove the css imports from the packages (see attachments), and manually import them directly in my app:

• decap-cms-widget-code+3.1.4.patch
• decap-cms-widget-map+3.1.4.patch

import 'ol/ol.css';
import 'codemirror/lib/codemirror.css';
import 'codemirror/theme/material.css';

Workaround

The esm build output should probably inline the CSS, as there isn't an industry standard for resolving css imports.

4. react-scroll-sync@0.9.0 is not compatible with React 19

This isn't specifically related to the esm build changes, but this should help fix React compatibility issues. The current version of react-scroll-sync is not compatible with React 19.

Error

TypeError: this.context.unregisterPane is not a function at ScrollSyncPane.componentWillUnmount

Workaround

add a local override to bump react-scroll-sync@0.11.2 to your package.json:

  "overrides": {
    "react-scroll-sync": "0.11.2"
  },

Proposed Fix

bump react-scroll-sync@^0.11.2 in decap-cms-core