/Knowledge/sources/honojs__hono/llms-full/websocket-helper-upgradewebsocket--f2fb40df9e52.md
WebSocket Helper: upgradeWebSocket() - hono-docs
WebSocket Helper: upgradeWebSocket() Source evidence: /Sources/honojs hono/provenance.md Canonical citation: https://hono.dev/llms full.txt upgradewebsocket...
WebSocket Helper: upgradeWebSocket()
Source evidence: /Sources/honojs__hono/provenance.md Canonical citation: https://hono.dev/llms-full.txt#upgradewebsocket
Summary
upgradeWebSocket() returns a handler for handling WebSocket. ```ts const app = new Hono() app.get( '/ws', upgradeWebSocket((c) => { return { onMessage(event, ws) { console.log(Message from client: ${event.data}) ws.send('Hello from s...
Content
upgradeWebSocket() returns a handler for handling WebSocket.
const app = new Hono()
app.get(
'/ws',
upgradeWebSocket((c) => {
return {
onMessage(event, ws) {
console.log(`Message from client: ${event.data}`)
ws.send('Hello from server!')
},
onClose: () => {
console.log('Connection closed')
},
}
})
)
Available events:
onOpen- Currently, Cloudflare Workers does not support it.onMessageonCloseonError
::: warning
If you use middleware that modifies headers (e.g., applying CORS) on a route that uses WebSocket Helper, you may encounter an error saying you can't modify immutable headers. This is because upgradeWebSocket() also changes headers internally.
Therefore, please be cautious if you are using WebSocket Helper and middleware at the same time.
:::
Metadata
{
"chunk_index": 0,
"citation": "https://hono.dev/llms-full.txt#upgradewebsocket",
"coverage_role": "overview",
"qualified_title": "Hono / llms-full / WebSocket Helper > `upgradeWebSocket()`",
"retrieved_at": "2026-07-02T05:51:01Z",
"section_index": 708,
"source_id": "/honojs/hono",
"source_type": "llms_full",
"target_label": "llms-full",
"title": "WebSocket Helper: upgradeWebSocket()",
"upstream_url": "https://hono.dev/llms-full.txt",
"version": "2026"
}
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