NDEFReader: scan() method

The scan() method of the {{DOMxRef("NDEFReader")}} interface activates a reading device and returns a {{jsxref("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.

Syntax

js-nolint

scan(options)

Parameters

options {{optional_inline}}
- : An object with the following properties:
  - signal
    - : An {{DOMxRef("AbortSignal")}} that allows cancelling this scan() operation.

Return value

A {{JSxRef("Promise")}} that resolves immediately after scheduling read operations for the NFC adapter.

Exceptions

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

AbortError {{domxref("DOMException")}}
- : Returned if the scan operation was aborted with the {{DOMxRef("AbortSignal")}} passed in the options argument.
InvalidStateError {{domxref("DOMException")}}
- : Returned if there's already an ongoing scan.
NotAllowedError {{domxref("DOMException")}}
- : Returned if the permission for this operation was rejected.
NotSupportedError {{domxref("DOMException")}}
- : Returned if there is no NFC adapter compatible with Web NFC or a connection cannot be established.

Examples

Handle scanning errors

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}.`);
  });