The scan() method of the NDEFReader interface activates a reading device and returns a Promise that either resolves when an NFC tag read operation is scheduled 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.

options Optional

An object with the following properties:

signal

An AbortSignal that allows cancelling this scan() operation.

A Promise that resolves immediately after scheduling read operations for the NFC adapter.

This method doesn't throw exceptions; instead, it rejects the returned promise, passing a DOMException whose name is one of the following:

AbortError DOMException

Returned if the scan operation was aborted with the AbortSignal passed in the options argument.

InvalidStateError DOMException

Returned if there's already an ongoing scan.

NotAllowedError DOMException

Returned if the permission for this operation was rejected.

NotSupportedError DOMException

Returned if there is no NFC adapter compatible with Web NFC or a connection cannot be established.

This example shows what happens when a scan promise rejects and readingerror is thrown.

const ndef = new NDEFReader();
ndef
  .scan()
  .then(() => {
    console.log("Scan started successfully.");
    ndef.onreadingerror = (event) => {
      console.log(
        "Error! Cannot read data from the NFC tag. Try a different one?",
      );
    };
    ndef.onreading = (event) => {
      console.log("NDEF message read.");
    };
  })
  .catch((error) => {
    console.log(`Error! Scan failed to start: ${error}.`);
  });