What is messenger app?
A messenger app, in the business-support sense, is the customer-facing chat surface embedded on a website. Intercom’s product name popularized the term. The messenger is what the visitor sees: the launcher button, the conversation panel, the history, the file uploads.
Standard features
Launcher button (the floating bubble), expandable conversation panel, message history persisted across sessions, file uploads, emoji reactions, typing indicators, read receipts, the ability to identify the visitor, theming to match the host brand.
Messenger vs widget
The two words are interchangeable in practice. "Widget" emphasizes the embed pattern (a small piece of UI on a host page). "Messenger" emphasizes the conversational nature (it is a messaging surface, like WhatsApp or iMessage).
The shadow-DOM detail
Modern messenger apps render inside a shadow DOM to avoid style collisions with the host page. CSS from the host site cannot leak in; CSS from the messenger cannot leak out. This matters because every site on the internet has its own CSS hell and the messenger needs to render correctly regardless.
See it working on message.com.
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