The write()
method of the NDEFReader
interface attempts to write an NDEF message to a tag and returns a Promise
that either resolves when a message has been written to the tag or rejects if a hardware or permission error is encountered. This method triggers a permission prompt if the "nfc" permission has not been previously granted.
NDEFReader.write(message);
NDEFReader.write(message, options);
A Promise
that either resolves when a message has been written to the tag or rejects if a hardware or permission error is encountered.
This method doesn't throw exceptions; instead, it rejects the returned promise, passing a DOMException
whose name
is one of the following:
-
AbortError
-
The scan operation was aborted with the AbortSignal
passed in the options
argument.
-
NotAllowedError
-
The permission for this operation was rejected or overwrite
is false
and there are already records on the tag.
-
NotSupportedError
-
There is no NFC adapter compatible with Web NFC, or the available NFC adapter does not support pushing messages, or connection can not be established.
-
NotReadableError
-
The UA is not allowed to access underlying NFC adapter (e.g., due to user preference).
-
NetworkError
-
Transfer failed after it already started (e.g., the tag was removed from the reader).
The following example shows how to write a DOMString
to an NFC tag and process any errors that occur.
const ndef = new NDEFReader();
ndef.write(
"Hello World"
).then(() => {
console.log("Message written.");
}).catch(error => {
console.log(`Write failed :-( try again: ${error}.`);
});
The following example shows how to write a record object (described above) to an NFC tag and process any errors that occur.
const ndef = new NDEFReader();
try {
await ndef.write({
records: [{ recordType: "url", data: "http://example.com/" }]
});
} catch {
console.log("Write failed :-( try again.");
};
It's sometimes useful to set a time limit on a write operation. For example, you ask the user to touch a tag, but no tag is found within a certain amount of time, then you time out.
const ndef = new NDEFReader();
ndef.onreading = (event) => console.log("We read a tag!");
function write(data, { timeout } = {}) {
return new Promise((resolve, reject) => {
const ctlr = new AbortController();
ctlr.signal.onabort = () => reject("Time is up, bailing out!");
setTimeout(() => ctlr.abort(), timeout);
ndef.addEventListener("reading", event => {
ndef.write(data, { signal: ctlr.signal }).then(resolve, reject);
}, { once: true });
});
}
await ndef.scan();
try {
await write("Hello World", { timeout: 5_000 });
} catch(err) {
console.error("Something went wrong", err);
} finally {
console.log("We wrote to a tag!");
}