subscribe-ui-event

subscribe-ui-event provides an cross-browser and performant way to subscribe to browser UI Events and some higher level events.

Instead of calling window.addEvenListener('scroll', eventHandler);, you can call subscribe('scroll', eventHandler), and it will help you hook eventHandler to window.scroll only once for multiple subscriptions.

The benefit is some global variables, such like document.body.scrollTop, can be retrieved only once for all subscriptions, which is better for performance. Throttling for all subscriptions is another benefit, which also can increase the performance.

The list of benefits:

1. Do throttling by default.
2. Provide requestAnimationFrame throttle for the need of high performance.
3. Attach to UI event only once for multiple subscriptions, and broadcast via eventemitter3,
4. Provide single access to UI variables (such like scrollTop) to avoid multiple reflows.

Install

ynpm install subscribe-ui-event

API

subscribe

Subscription subscribe(String eventType, Function callback, Object? options)

Provide throttled version of window or document events, such like scroll, resize and visibilitychange to subscribe. It also provides some higher, compound events, such like viewportchange, which combines scroll, resize and visibilitychange events.

Note on IE8 or the below, the throttle will be turned off because the event object is global and will be deleted for setTimeout or rAF.

Example:

var subscribe = require('subscribe-ui-event').subscribe;
function eventHandler (e, payload) {
    // e is the native event object and
    // payload is the additional information
    ...
}
// 50ms throttle by default
var subscription = subscribe('scroll', eventHandler);
// remove later
subscription.unsubscribe();

Addtional Payload

The format of the payload is:

{
    type: <String>, // could be 'scroll', 'resize' ...
    // you need to pass options.enableScrollTop = true to subscribe to get the following data
    scroll: {
        top: <Number>, // The scroll position, i.g., document.body.scrollTop
        prevTop: <Number>, // The previous scroll position
        delta: <Number> // The delta of scroll position, it is helpful for scroll direction
    }
}

Options

options.throttleRate allows of changing the throttle rate, and the default value is 50 (ms). Set 0 for no throttle. On IE8, there will be no throttle, because throttling will use setTimeout or rAF to achieve, and the event object passed into event handler will be overwritten.

options.context allows of setting the caller of callback function.

options.useRAF = true allows of using requestAnimationFrame instead of setTimeout.

options.enableScrollInfo = true allows of getting scrollTop.

options.enableResizeInfo = true allows of getting width and height of client.

eventType could be one of the following:

1. scroll - window.scoll
2. scrollStart - The start window.scoll
3. scrollEnd - The end window.scoll
4. resize - window.resize
5. resizeStart - The start window.resize
6. resizeEnd - The end window.resize
7. visibilitychange - document.visibilitychange
8. viewportchange - scroll + resize + visibilitychange

unsubscribe

Void unsubscribe(String eventType, Function callback)

Unsubscribe an event. Note that all subscriptions with the same eventHandler and the same event type will be unsubscribed together even if they have different options.

License

This software is free to use under the BSD license. See the LICENSE file for license text and copyright information.