Authors:
- Kenneth Christiansen
- Zoltan Kis
- Francois Beaufort
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Web NFC aims to provide sites the ability to read and write to nearby NFC (Near Field Communication) tags in a secure and privacy preserving manner.
NFC consists of a rather large set of technologies, so for this first iteration of the API the focus has been on supporting the NFC Data Exchange Format aka NDEF, a lightweight binary message format, as it works across different tag formats.
Web NFC is only available to top-level, secure browsing contexts, and origins must first request the “nfc” permission while handling a user gesture. To then perform a read or write, the web page must be visible when the user touches an NFC tag with their device. The browser uses haptic feedback to indicate a tap. Access to the NFC radio is blocked if the display is off or the device is locked. For backgrounded web pages, receiving and pushing NFC content are suspended.
We believe Web NFC is an easy to use API that web developers will be comfortable with, and at the same time that it is low-level and flexible enough so that users can get the full potential out of NDEF and even integrate with legacy solutions.
Read and write to NFC tags/cards using the NDEF standards, in an easy webby manner, while being flexible enough to integrate easily with existing NDEF based solutions.
Make sure the API is extendable to cover more NFC use-cases, like non-NDEF, in the future.
In this version of the API, proprietary NFC technologies used in hotel keys, e-passports etc are not supported. Automatic handling of NFC content, such as opening or saving files, making calls or saving contacts (with “smart posters”), or joining WiFi or Bluetooth networks (NFC handover) is not supported.
NFC (with NDEF) is not secure for authenticity or integrity. NDEF tags are like post-it notes, anyone can read them, and unless read-only, anyone can write them. Web NFC does not handle automatic encryption or signing of NFC content (with NDEF signatures): handling PKI infrastructure is left to applications.
The API has gone through multiple iterations and have had feedback from Mozilla, Google as well as web developers.
The API is modern and follows other hardware connectivity APIs in the use of DataView to expose data.
The full API can be seen here: https://w3c.github.io/web-nfc/#idl-index
Lots of examples can be found here: https://w3c.github.io/web-nfc/#examples
Among different use-cases, NFC allows users to take their NFC enabled device such as a phone and touch NFC tags (sticker, card and the like). The platform, or a certain application can then at this moment read the content and write new content back.
Web NFC allows to build web experiences that can do the above, thus exchange data between the web enabled device and NFC tags.
Data read from NFC tags can come from unknown sources and thus should be treated like that by web developers. This is no different than treating user input and data such as JSON, fetched from a remote server.
The NDEF signature records, gives the web site the possibility of verifying the authenticity and integrity of data within the NDEF message and only deal with data it trusts.
Additionally, Web NFC integrates well with other existing APIs:
The close integration with the Permissions API allows web developers to prompt users, when required, about granting access to Web NFC. It means sending and receiving info when users tap NFC devices can be done smoothly once permission is granted.
const ndef = new NDEFReader();
async function startScanning() {
await ndef.scan();
ndef.onreading = event => {
/* handle NDEF messages */
};
}
const nfcPermissionStatus = await navigator.permissions.query({ name: "nfc" });
if (nfcPermissionStatus.state === "granted") {
// NFC access was previously granted, so we can start NFC scanning now.
startScanning();
} else {
// Show a "scan" button.
document.querySelector("button").style.display = "block";
document.querySelector("button").onclick = event => {
// Prompt user to allow UA to send and receive info when they tap NFC devices.
startScanning();
};
}Web NFC is following the spirit of other hardware communication APIs like Web Bluetooth and Web USB in that it offers secure low level access with no magic and instead exposes data as a DataView as well as requires text to be encoded and decoded using TextEncoder/TextDecoder, which allows handling cases where the text might even be in UTF-16 do to existing real life implementations.
const ndef = new NDEFReader();
await ndef.scan();
ndef.onreading = event => {
const externalRecord = event.message.records.find(
record => record.type == "example.com:smart-poster"
);
let action, text;
for (const record of externalRecord.toRecords()) {
if (record.recordType == "text") {
const decoder = new TextDecoder(record.encoding);
text = decoder.decode(record.data);
} else if (record.recordType == "act") {
action = record.data.getUint8(0);
}
}
console.log({text, action});
};Using the AbortController primitive allows web developers to easily abort NFC operations and other operations that use it. It makes it easy to cancel multiple things, especially when switching views in a single-page application for instance.
const abortController = new AbortController();
abortController.signal.onabort = event => {
// All NFC operations have been aborted.
};
const ndef = new NDEFReader();
await ndef.scan({ signal: abortController.signal });
await ndef.write("foo", { signal: abortController.signal });
document.querySelector("#abortButton").onclick = event => {
abortController.abort();
};Web NFC functionality is allowed only for the document of the top-level browsing context, which must be visible. Thanks to the Page Visibility API, web developers can track when it document visibility changes.
document.onvisibilitychange = event => {
if (document.hidden) {
// All NFC operations are automatically suspended when document is hidden.
} else {
// All NFC operations are resumed, if needed.
}
};NDEF (NFC Data Exchange Format) comes with a set of standard records with data encoded in particular ways, like text which also encode the encoding and language name, and even smart-poster, which can contain icons and descriptions in multiple languages.
It would have been possible to just expose these as separate objects, each with a set of properties. That would solve the common go-to examples for NFC, but it would also be limiting as it would be impossible (at least without an additional API) to read and create custom or slightly different records.
This was attempted in an earlier effort to add NFC support to the web platform: https://www.w3.org/2012/nfc/web-api/#ndefrecordsmartposter-interface
The common records, though often used for illustration, are not that popular and the power really lies in being able to store your own data in the most efficient way, as well as being able to interact with existing solutions deployed in the wild.
Instead of having two sets of APIs, we decided that it was best to offer a more low-level API that is still easy to use for simple cases like the standardized NDEF records.
Other connectivity APIs currently rely on attaching themselves to the navigator object/namespace, like Web Bluetooth, Web USB, etc. Unlike these APIs, the newer Generic Sensor APIs don’t attach themselves to the navigator object/namespace and have separate and dedicated objects like Accelerometer, Gyroscope, etc.
We decided to follow this newer pattern as it allows node.js to implement the same API, and have it loaded as a separate module. People working on Web Assembly are also advocating for this patterns as it might be able to turn such globals into modules in the future, at least when accessed from WASM.
The reader and writer objects existed separately when scan filters were supported, but after filters have been abandoned, they have been merged into one single object.
As an example, initially we used names like NFCReader and added required reading APIs. In order to add additional APIs for alternative NFC technologies (say NFC-A), adding these to the reader object could make it less straightforward to use for users and may result in currently API design that later if found out to be insufficient for the future additions.
Some native APIs have added all functionality to the same objects, but other APIs have separated NDEF from other tag technologies and we have decided that that leads to the easiest to understand API, as well as minimizes the risk of running into API issues when extending the API in the future.
- Chrome: Positive (part of Project Fugu)
- Firefox: Positive in the FirefoxOS days, since then, no signals
- Safari: Negative
- Edge: No signals
From speaking about the feature at multiple events over the years, it is clear that web developers have been quite positive about the ability to use NFC from the web.
The OT feedback was the filtering feature was not needed very much, and applications can easily implement it.
Once scan filtering was removed, there was no point in keeping separate objects
for reading and writing NDEF tags. Hence NDEFWriter.write became
NDEFReader.write.
When a tag is written, it is also read. With merging the reading and writing objects, this option became unneeded. There is an example included on how to ignore reads when writing.
Since the merge of NDEFWriter and NDEFReader, the former onerror event on
NDEFReader still relates to scans, but it could be interpreted to be also
relevant on writes, which is not the case. This change clarifies the error is
only relevant for scans.
These changes mark the Chrome Origin Trial complete.
Thanks to Jeffrey Yasskin, Anne van Kesteren, Anssi Kostiainen, Domenic Denicola, Daniel Ehrenberg, Jonas Sicking, Don Coleman, Salvatore Iovene, Rijubrata Bhaumik, Elena Reshetova, Wanming Lin and Han Leon for their contributions.