Fix ESM bundle missing named exports

[Copilot]

The ESM bundle (dist/mqtt.esm.js) was not exporting named exports like connect, connectAsync, etc., causing import errors in browser environments using ES modules.

Root cause: esbuild was bundling a CommonJS entry point for ESM output. When bundling CJS modules with export * re-exports, esbuild cannot convert module.exports to ES6 export statements.

Changes:

• Created src/index.esm.ts: Dedicated ESM entry point using native ES6 export syntax

  export { default } from './mqtt'
  export { connect, connectAsync, MqttClient, Client, ... } from './mqtt'
  export * from './mqtt'

• Updated esbuild.js: ESM bundle now uses build/index.esm.js instead of build/index.js

• Enhanced src/index.ts: Added explicit named re-exports for improved CommonJS compatibility

The generated ESM bundle now properly exports all named exports while maintaining backward compatibility.

Example usage:

import { connect } from 'mqtt'  // Now works in ESM environments

Original prompt

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This section details on the original issue you should resolve

<issue_title>[Bug]: 5.14.0does not provide an export named 'connect'</issue_title>
<issue_description>### MQTTjs Version

5.14.0

Broker

暂不详

Environment

Browser

Description

Minimal Reproduction

does not provide an export named 'connect'

Debug logs

does not provide an export named 'connect'</issue_description>

<agent_instructions>Fix issue browser bundle not exporting connect function like nodejs </agent_instructions>

Comments on the Issue (you are @copilot in this section)

@robertsLando @xuzhongfei how are you importing mqtt? Does previous version works?

• Fixes [Bug]: 5.14.0does not provide an export named 'connect' #2022

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