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    1.7.1 • Public • Published

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    Send messages between browser tabs

    sysend.js is a small library that allows to send messages between pages that are open in the same browser. It also supports Cross-Domain communication. The library doesn't have any dependencies and uses the HTML5 LocalStorage API or BroadcastChannel API. If your browser don't support BroadcastChannel (see Can I Use) then you can send any object that can be serialized to JSON. With BroadcastChannel you can send any object (it will not be serialized to string but the values are limited to the ones that can be copied by the structured cloning algorithm). You can also send empty notifications.

    Tested on:

    GNU/Linux: in Chromium 34, FireFox 29, Opera 12.16 (64bit)
    Windows 10 64bit: in IE11 and Edge 38, Chrome 56, Firefox 51
    MacOS X El Captain: Safari 9, Chrome 56, Firefox 51

    Note about Safari 7+ and Cross-Domain communication

    All cross-domain communication is disabled by default with Safari 7+. Because of a feature that block 3rd party tracking for iframe, and any iframe used for cross-domain communication runs in sandboxed environment. That's why this library like any other solution for cross-domain comunication, don't work on Safari.


    Include sysend.js file in your html, you can grab the file from npm:

    npm install sysend

    or bower

    bower install sysend

    you can also get it from CDN:

    or jsDelivr:

    jsDelivr will minify the file. From my testing it's faster then


    window.onload = function() {
        sysend.on('foo', function(data) {
        var input = document.getElementsByTagName('input')[0];
        document.getElementsByTagName('button')[0].onclick = function() {
            sysend.broadcast('foo', { message: input.value });

    If you want to add support for Cross-Domain communication, you need to call proxy method with url on target domain that have proxy.html file.


    on Firefox you need to add CORS for the proxy.html that will be loaded into iframe (see Cross-Domain LocalStorage)

    if you want to send custom data you can use serializer (new in 1.4.0). Example serializer can be json-dry.

    sysend.serializer(function(data) {
        return Dry.stringify(data);
    }, function(string) {
        return Dry.parse(string);


    Open this demo page in two tabs/windows (there is also link to other domain).


    sysend object:

    • on(name, callback) - callback(object, name) - add event handler for specified name.
    • off(name [, callback]) - remove event handler for given name, if callback is not specified it will remove all callbacks for given name.
    • broadcast(name [, object]) - send any object and fire all events with specified name (in different pages that register callback using on). You can also just send notification without an object.
    • emit(name, [, object]) - same as broadcast but also invoke the even on same page (new in 1.5.0).
    • proxy(url) - create iframe proxy for different domain, the target domain/url should have proxy.html file. If url domain is the same as page domain, it's ignored. So you can put both proxy calls on both domains (new in 1.3.0).
    • serializer(to_string, from_string) - add serializer and deserializer functions (new in 1.4.0).
    • post(<window_id>, [, object]) - send any data to other window (new in 1.6.0).
    • list() - function return Promise of objects {id:<UUID>, primary} for other windows, you can use those to send message with post() (new in 1.6.0).
    • track(event, callback) - track specific event (new in 1.6.0), avilable events: "open", "close", "primary", "secondary", "message", callback is a function that accepts single object as argument:
      • "open": {count, primary, id}.
      • "close": {count, primary, id, self}.
      • "primary" and "secondary" no argument is given.
    • untrack(event [,callback]) - remove tracking callback, if no function is given it will remove all callbacks for a given event (new in 1.6.0).
    • isPrimary() - function that return true/false depend if window is primary (first window opened or last that remain) (new in 1.6.0).

    To see details of using the API, see demo.html source code or TypeScript definition file.


    Copyright (C) 2014-2021 Jakub T. Jankiewicz
    Released under the MIT license

    This is free software; you are free to change and redistribute it.
    There is NO WARRANTY, to the extent permitted by law.


    npm i sysend

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