The port property of a WorkerLocation object returns the port of the worker’s location as a string. Learn self.location.port, how it differs from host and hostname, why default ports can be empty, and what blob workers report—with five examples and try-it labs.
Instance property
String
self.location
Read-only
Web Workers only
Baseline widely
A port is the number that identifies which service on a host is being contacted—for example 8080 in http://localhost:8080/. Inside a worker, self.location.port returns that port for the worker script URL as a string.
MDN’s classic idea: on a worker related to http://localhost:8080/, location.port can look like "8080".
Default ports often return "" (empty string)—not "80" or "443". For hostname plus port when shown, use host.
port PropertyA read-only instance property on WorkerLocation that returns the worker’s port as a string.
"8080", "3002", or "").self.location.port or location.port inside the worker.Read the property inside a worker script:
const result = self.location.port;
// e.g. "8080"A string.
// Inside a Web Worker
const result = self.location.port;
self.postMessage(result);| Goal | Code / note |
|---|---|
| Read port | self.location.port |
| Return type | String |
| MDN example shape | "8080" |
| Default http/https | Often "" (empty) |
| Send to main | self.postMessage(location.port) |
| MDN status | Baseline Widely available (since July 2015) |
Four facts to remember about WorkerLocation.port.
portString
in workerself.location
noRead-only
widelySince Jul 2015
Examples follow MDN WorkerLocation.port. Labs use blob workers and compare port with related URL parts.
Read the port the MDN way.
self.location.port (MDN Idea)Post the worker port string to the main thread.
const result = self.location.port;
// e.g. "8080"
self.postMessage(result);The try-it lab posts the live blob worker’s port plus the MDN sample string for comparison.
port vs host vs hostnamePort is only the number; host may combine hostname and port.
self.postMessage({
port: location.port,
host: location.host,
hostname: location.hostname
});Use port when you only need the number; use host when you want hostname + port together.
See how blob workers and default ports behave.
Log port together with protocol and href for blob workers.
self.postMessage({
port: location.port,
protocol: location.protocol,
href: location.href
});Blob workers often report an empty port—not like MDN’s "8080" sample. Always inspect the live value.
Check whether port is an empty string (common for defaults / blobs).
self.postMessage({
port: location.port,
isEmpty: location.port === ""
});Treat empty port as “default / not shown,” not as an error. A dedicated worker on :8080 would usually show a non-empty string.
Post the worker port; compare it with window.location.port.
// Worker
self.postMessage(location.port);
// Main
worker.onmessage = (e) => {
console.log("worker:", e.data);
console.log("page:", location.port);
};The page port often matches your local server (e.g. 3002); the blob worker port may still be empty.
8080.host and hostname when diagnosing URLs.Main creates a Worker with an http(s), blob, or other script URL.
Inside the worker, self.location describes that absolute script URL.
location.port returns the port string (or "" for defaults).
Compare, log, or postMessage the port to the main thread.
WorkerLocation / self.location)."".WorkerLocation.port is marked Baseline Widely available on MDN (since July 2015). Logos use the shared browser-image-sprite.png sprite from this project. It is only available in Web Workers.
Returns the worker's port as a string. Read it with self.location.port inside a worker.
Bottom line: Read location.port inside the worker—empty often means default port. Pair with host and hostname when debugging.
WorkerLocation.port is the worker-side port string for the script URL. Read it inside the worker, expect empty values for defaults and many blob demos, and use host when you need hostname + port together.
Continue with protocol, pathname, host, or the JavaScript hub.
port only inside a workerwindow.location.port on the main threadhost and href alongside portpostMessage to surface the value on the pageWorkerLocation on the main threadlocation.port in a worker (read-only)"443"8080 exampleport with the full host stringWorkerLocation.portThe worker script’s port, as a string.
port string
APIself.location
Contextno assign
Ruledefaults / blobs
Gotchasince Jul 2015
StatusMDN’s example uses a non-default port 8080 so the property is easy to see. On plain https:// sites, location.port is often "" even though the connection uses port 443.
Learn how to read the worker's protocol string.
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