NDEFReader.write()

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.

message

The message to be written, one of DOMString, BufferSource, or an array of records. A record has the following members:

data Optional

Contains the data to be transmitted, one of a string, a BufferSource, or an array of nested records.

encoding Optional

A string specifying the record's encoding.

id Optional

A developer-defined identifier for the record.

lang Optional

A valid BCP47 language tag.

mediaType Optional

A valid MIME type.

recordType

A string indicating the type of data stored in data. It must be one of the following values:

"absolute-url"

An absolute URL to the data.

"empty"

An empty NDEFRecord.

"mime"

A valid MIME type.

"smart-poster"

A smart poster as defined by the NDEF-SMARTPOSTER specification.

"text"

Text as defined by the NDEF-TEXT specification.

"unknown"

The record type is not known.

"URL"

A URL as defined by the NDEF-URI specification.

options Optional

An object with the following properties:

• overwrite -- A Boolean specifying whether or not existing records should be overwritten, if such exists.
• signal -- An optional AbortSignal that allows the current write operation to be canceled.

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 {
  // Let's wait for 5 seconds only.
  await write("Hello World", { timeout: 5_000 });
} catch(err) {
  console.error("Something went wrong", err);
} finally {
  console.log("We wrote to a tag!");
}