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    0.2.1 • Public • Published


    Share data beyond the boundaries of the browser.

    Build status

    By utilizing the DataTransfer API capabilities to transfer data to applications, Transmat is enabling your web app to interact beyond the boundaries of the browser. This technique is compatible all modern desktop browsers since IE11.

    Transmat will help you setting up the necessarily drag-drop and copy-paste interactions, and help you in transferring (both transmitting and receiving) the data.

    This is not an officially supported Google product.

    Transmitting data

    The DataTransfer payload consists of simple string-based key value pairs. When providing mime-types keys and their expected data, new integrations can happen, sometimes for free.

    import {Transmat, addListeners} from 'transmat';
    addListeners(myElement, 'transmit', event => {
      const transmat = new Transmat(event);
        'text/plain': 'This will show up in text fields',
        'text/html': '<img src="" />',
        'text/uri-list': '',
        'application/': {foo: 'bar'},

    When transferring the example from above, you can expect the following to happen depending on the receiving target;

    • WYSIWYG inputs like contentEditable, Google Docs, Gmail, Apple Pages will use text/html data, and fallback to text/plain.
    • Text inputs like textareas, VSCode, will show text/plain.
    • Browsers will navigate the URLs listed in the text/uri-list data.

    Receiving data

    You can receive the DataTransfer payload by listening to the drop and paste events.

    import {Transmat, addReceiveListeners} from 'transmat';
    addListeners(myElement, 'receive', event => {
      const myCustomMimeType = 'application/';
      const transmat = new Transmat(event);
      if(transmat.hasType(myCustomMimeType) && transmat.accept()) {
        const dataString = transmat.getData(myCustomMimeType);
        const data = JSON.parse(dataString);

    Connecting the web, and beyond

    The project's vision is to connect the web. By promoting the use of JSON-LD data transfers, applications will be able to speak the same language independently from their implementation. With growing adoption, users will be able to transfer data without friction to any other applications, across the web. How cool is that?

    import {Person} from 'schema-dts';
    import {Transmat} from 'transmat';
    import * as jsonLd from 'transmat/lib/json_ld';
    // When transmitting...
    const transmat = new Transmat(event);
    transmat.setData(jsonLd.MIME_TYPE, jsonLd.fromObject<Person>({
      "@type": "Person",
      "name": "Rory Gilmore",
      "image": "",
      "address": {
        "@type": "PostalAddress",
        "addressCountry": "USA",
        "addressRegion": "Connecticut",
        "addressLocality": "Stars Hollow"
    // .. and when receiving
    if (transmat.hasType(jsonLd.MIME_TYPE)) {
      const person = jsonLd.getData<Person>(jsonLd.MIME_TYPE);

    Observing transfer events

    You can make use of the included TransmatObserver class to respond to drag activity. Use this to for example highlight valid drop areas.

    import {TransmatObserver, Transmat} from 'transmat';
    const obs = new TransmatObserver(entries => {
      for (const entry of entries) {
        const transmat = new Transmat(entry.event);
        if(transmat.hasMimeType(myCustomMimeType)) {
'drag-over', entry.isTarget);
'drag-active', entry.isActive);

    Some concerns


    Drag-drop and copy-paste are native interactions, with roots back to the first GUIs about 40 years ago. On the desktop, these are common operations that users will do often. Think about organizing files, dragging files to tools to open them, etc. On the web, this is uncommon.

    We will need to educate users about this new capability, and ideally come up with UX patterns to make this recognizable.


    Drag-drop is not a very accessible interaction, but the DataTransfer API works with copy-paste too.

    Security and privacy

    The data stored in the DataTransfer will be available to any application on the user's device. Keep this in mind when transferring sensitive data. Web applications can only read the data payload on drop. While dragging, only the keys (mime-types) are exposed to the webpage that is being dragged over.

    Receiving data should be treated like any other user input; sanitize and validate before using.

    Known quirks

    • Chrome strips newlines in text/uri-list. For now, you can only use this to transfer a single URI.
    • Transferring files generated using new File() doesn't seem to be supported well enough.
    • Web applications can only read the payload (using getData) when finishing the transfer by dropping or pasting. While dragging, only the types can be read.
    • The DataTransfer data keys are transformed to lowercase.
    • Mobile devices have poor support. iOS ignores DataTransfer, Chrome on Android only supports text/plain.


    Use GitHub issues for filing bugs. Follow @jorikdelaporik on Twitter for occasional updates around the project.




    npm i transmat

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