This is documentation for the next version of Grafana k6 documentation. For the latest stable release, go to the latest version.

Documentation Grafana k6 JavaScript API k6/x/tcp Socket Socket.on( event, listener )

Socket.on()

Registers an event listener for a socket lifecycle event. All event handlers execute in the context of the k6 VU event loop.

Only one listener per event type is supported. Calling on() for an event that already has a listener replaces the previous one.

Signature

JavaScript Copy

socket.on(event, listener)

Parameters

Events

connect

Emitted when the socket successfully establishes a connection to the remote server.

Signature

JavaScript Copy

socket.on("connect", () => {
  // Connection established
})

data

Emitted when data is received from the remote endpoint. The data is provided as a Uint8Array.

Signature

JavaScript Copy

socket.on("data", (data) => {
  // data is Uint8Array
})

Parameters

close

Emitted when the socket connection is fully closed, either by the local or remote side. This is the final event in the socket lifecycle and is emitted exactly once per socket.

Signature

JavaScript Copy

socket.on("close", () => {
  // Connection fully closed
})

error

Emitted when a socket error occurs, such as a connection failure or network issue.

Signature

JavaScript Copy

socket.on("error", (error) => {
  // Handle error
})

Parameters

timeout

Emitted when the socket times out due to inactivity as configured by setTimeout(). The socket doesn’t automatically close the connection—call destroy() to close it.

Signature

JavaScript Copy

socket.on("timeout", () => {
  // Inactivity timeout reached
})

Returns

void

Example

JavaScript Copy

import { Socket } from "k6/x/tcp"

export default async function () {
  const socket = new Socket()

  const closed = new Promise((resolve) => {
    socket.on("close", () => {
      console.log("Connection closed")
      resolve()
    })
  })

  socket.on("connect", () => {
    console.log("Connected to server")
  })

  socket.on("data", (data) => {
    const str = String.fromCharCode.apply(null, new Uint8Array(data))
    console.log("Received:", str)
    socket.destroy()
  })

  socket.on("error", (err) => {
    console.error("Socket error:", err)
    socket.destroy()
  })

  socket.on("timeout", () => {
    console.log("Socket timed out")
    socket.destroy()
  })

  await socket.connect(8080, "example.com")
  await socket.write("Hello, server!")

  await closed
}