transform-sdk/js: add typings

Add an NPM package for our javascript SDK, this mostly is to provide
typings and documentation in IDEs/LSPs

Signed-off-by: Tyler Rockwood <rockwood@redpanda.com>

src/transform-sdk/js/module/index.d.ts

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+// Copyright 2024 Redpanda Data, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// RecordData is a wrapper around the underlying raw data
+// in a record.
+//
+// Similar to a JavaScript Response object.
+export interface RecordData {
+  // Parse the data as JSON.
+  //
+  // This is a more efficent version of JSON.parse(text());
+  //
+  // @throws if the payload is not valid JSON
+  // @returns the parsed JSON
+  json(): any;
+  // Parse the data as a UTF-8 string.
+  //
+  // @throws if the payload is not valid UTF-8
+  // @returns the parsed string
+  text(): string;
+  // Return the data as a raw byte array.
+  array(): Uint8Array;
+}
+
+// Records may have a collection of headers attached to them.
+//
+// Headers are opaque to the broker and are purely a mechanism for the
+// producer and consumers to pass information.
+export interface RecordHeader {
+  // The key of this header.
+  readonly key?: string | ArrayBuffer | Uint8Array | RecordData | null;
+  // The value of this header.
+  readonly value?: string | ArrayBuffer | Uint8Array | RecordData | null;
+}
+
+// A record within Redpanda.
+//
+// Records are generated as a result of any transforms that act upon
+// a WrittenRecord.
+export interface Record {
+  // The key for this record.
+  readonly key?: string | ArrayBuffer | Uint8Array | RecordData | null;
+  // The value for this record.
+  readonly value?: string | ArrayBuffer | Uint8Array | RecordData | null;
+  // The headers attached to this record.
+  readonly headers?: RecordHeader[];
+}
+
+// Records may have a collection of headers attached to them.
+//
+// Headers are opaque to the broker and are purely a mechanism for the
+// producer and consumers to pass information.
+//
+// It is similar to a RecordHeader, expect that it only contains 
+// RecordData or null.
+export interface WrittenRecordHeader {
+  // The key for this header.
+  readonly key?: RecordData | null
+  // The value for this header.
+  readonly value?: RecordData | null
+}
+
+// A persisted record written to a topic within Redpanda.
+//
+// It is similar to a Record, expect that it only contains RecordData 
+// or null.
+export interface WrittenRecord {
+  // The key for this record.
+  readonly key: RecordData | null;
+  // The value for this record.
+  readonly value: RecordData | null;
+  // The headers for this record.
+  readonly headers: RecordHeader[];
+}
+
+// An even generated after a write event within the broker.
+export interface OnRecordWrittenEvent {
+  // The record that was written as part of this event.
+  readonly record: WrittenRecord;
+}
+
+// A writer for transformed records that are output to the destination 
+// topic.
+export interface RecordWriter {
+  // Write a record to the output topic.
+  //
+  // @throws if there are errors writing the record.
+  write(record: Record): void;
+}
+
+// The callback type for OnRecordWritten
+export type OnRecordWrittenCallback = (event: OnRecordWrittenEvent, writer: RecordWriter) => void;
+
+// Register a callback to be fired when a record is written to the 
+// input topic.
+//
+// This callback is triggered after the record has been written,
+// fsynced to disk and the producer acknowledged.
+//
+// This method should be called in your script's entrypoint.
+//
+// @example
+// import {onRecordWritten} from "@redpanda-data/transforms";
+//
+// // Copy the input data to the output topic.
+// onRecordWritten((event, writer) => {
+//   writer.write(event.record);
+// });
+export function onRecordWritten(cb: OnRecordWrittenCallback): void;
+

src/transform-sdk/js/module/index.js

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+// Copyright 2024 Redpanda Data, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+
+// This is a stub that does nothing.
+// When deployed in broker this function is 
+// provided by the JavaScript runtime.
+export function onRecordWritten(cb) {}

src/transform-sdk/js/module/package.json

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+{
+  "name": "@redpanda-data/transforms",
+  "version": "0.1.0",
+  "license": "Apache-2.0",
+  "main": "index.js",
+  "typings": "index.d.ts",
+  "module": "index.js",
+  "files": [
+    "index.js",
+    "index.d.ts",
+  ],
+  "publishConfig": {
+    "access": "public"
+  },
+  "engines": {
+    "node": ">=14"
+  },
+  "repository": "github:redpanda-data/redpanda",
+}