IconVault's Channel Messaging playground builds real `MessageChannel` ports: two entangled ports trade structured-cloned payloads in the page, and a second demo transfers a port into a genuine Web Worker (created from a Blob URL) that echoes messages back. A deliberate DataCloneError demo shows why functions cannot cross a port. It is free and runs fully in your browser.

MessageChannel is the plumbing behind iframe-to-parent widgets, worker offloading, and cross-context libraries: one side of a port can be transferred to another context while staying a private two-way pipe. The lab makes the entanglement rule tangible (each port only hears the other), proves structured cloning with nested objects and dates, and shows the transfer-list pattern you need for worker communication.