cap2UI5 vs. abap2UI5

They are the same framework. The question is not which framework you want but which runtime your code should live in — and that is usually decided for you by where your data is.

What is identical

Not "compatible" — identical, because it is the same code:

• the same frontend. The UI5 frontend ships inside @abap2ui5/node-runtime, straight from upstream's repository. Same bundle, same custom controls, same frontend actions, same boot;
• the same backend. Upstream's ABAP, downported and transpiled over open-abap. Not a port of it — it;
• the same wire. One PROTOCOL version, stamped by the same code that reads it;
• the same concepts. Roundtrips, the draft chain, the app stack, value helps as apps, one class per app;
• the same API. The client an app's main( client ) receives is z2ui5_if_client under its ABAP method names, and the view builder is z2ui5_cl_ui5_view_builder. abap2UI5's documentation of a method is the documentation of the JavaScript one.

The browser cannot tell which side answers.

This used to be a longer and more careful section

It listed the framework version this project had pinned, the API differences that version implied, and which examples were affected. None of that applies any more: there is no separate version to pin, because there is no second implementation to keep in step. See Where cap2UI5 Comes From.

What differs

	abap2UI5	cap2UI5
language	ABAP	JavaScript
runs on	an SAP system (NetWeaver, S/4, BTP ABAP)	Node.js, as a CAP plugin
deployment	abapGit into a system	npm i into a CAP project
data access	Open SQL	cds.ql, and CAP's remote services
session state	Z2UI5_T_01	cap2ui5.Drafts, a CDS entity in your database
identity	sy-uname	cds.context.user.id
client calls	client->check_on_navigated( )	client.check_on_navigated()
parameters by name	_event( val = `GO` t_arg = … )	one object: _event({ val: "GO", t_arg: [ … ] })
binding	_bind( name ) — the attribute, by reference	_bind("name") — the field, by name
view	z2ui5_cl_ui5_view_builder	the same builder, or a UI5 XML string

The full mapping is in Migrating from abap2UI5.

The same app, twice

" abap2UI5
METHOD z2ui5_if_app~main.
  IF client->check_on_navigated( ).
    client->view_display( ... ).
  ELSEIF client->check_on_event( `GO` ).
    client->message_box_display( |Hello { name }| ).
  ENDIF.
ENDMETHOD.

// cap2UI5
main(client) {
  if (client.check_on_navigated()) {
    client.view_display(/* … */);
  } else if (client.check_on_event("GO")) {
    client.message_box_display(`Hello ${this.name}`);
  }
}

Line for line. The languages part company in two places: ABAP names its arguments where JavaScript passes one object with the same names, and _bind( name ) becomes client._bind("name") because JavaScript cannot match a value by reference. That is close enough for a machine to do it: npx --no-install cap2ui5 abap2js translates an abap2UI5 app class into a cap2UI5 app, line for line, and refuses what it does not know rather than guess — see Migrating from abap2UI5. @cap2ui5/samples is 71 of abap2UI5's samples as cap2UI5 apps, 69 of them translated that way.

Which one do I want?

Your data is in an SAP system → abap2UI5. Running the UI where the data is avoids an integration you would otherwise have to build and secure.

Your data is in CAP → cap2UI5. Your apps read it with cds.ql, share the project's authentication, and a plain OData service can sit beside them on the same tables.

Both → both. The frontend is the same, the concepts are the same, and a developer moving between them is reading the same documentation.

Does the CAP side lag behind?

Not structurally. The runtime is a dependency: a new abap2UI5 release is a version bump, and it brings the backend and the frontend together. There is no port to catch up, no pipeline to re-run, nothing to re-transpile by hand.

The client covers every method of z2ui5_if_client — the plugin's tests hold it to the interface, so a method upstream adds shows up there as a failing test — the test reads the interface from the runtime it boots — rather than as a gap an app finds. client.raw, the transpiled interface itself, remains the escape hatch.

Next

• Migrating from abap2UI5 — the translation table, and abap2js
• Client API — every method of z2ui5_if_client
• Where cap2UI5 Comes From — why this is a host and not a port