WebTransport: reliability property
Baseline 2026
Newly available
Since November 2026, this feature works across the latest devices and browser versions. This feature might not work in older devices or browsers.
Secure context: This feature is available only in secure contexts (HTTPS), in some or all supporting browsers.
Note: This feature is available in Web Workers.
The reliability read-only property of the WebTransport interface indicates whether the connection supports reliable transports only, or whether it also supports unreliable transports (such as UDP).
Value
A string with one of the following values:
pending-
The connection has not yet been established. The reliability is not yet known.
reliable-only-
The connection only supports reliable transports.
supports-unreliable-
The connection supports both unreliable and reliable transports.
Examples
js
const url = "https://example.com:4999/wt";
async function initTransport(url) {
// Initialize transport connection
const transport = new WebTransport(url);
// Once ready fulfills the connection can be used
// Prior to this the reliability is "pending"
await transport.ready;
if (transport.reliability === "reliable-only") {
// Use connection only with reliable transports
} else {
// Use connection with either reliable or unreliable transports.
}
// …
}
Specifications
| Specification |
|---|
| WebTransport # dom-webtransport-reliability |