With subscribe-ui-event, instead of calling multiple window.addEventListener('scroll', eventHandler); by different components, call subscribe('scroll', eventHandler). It will only add a single event listener and dispatch event to those who subscribe to the event via eventemitter3.

npm install subscribe-ui-event

Why a single event? More performant and less memory consumption.

The jsperf runs 10 addEventListener and 10 non-throttling subscribe, and the outcome is that the ops/sec of subscribe is slightly less. But in regular case, you will use throttling subscribe, and it will be more performant.

For 10 addEventListener, the difference of memory consumption between peak and trough is about 4.1K.

For 10 subscribe, the difference of memory consumption between peak and trough is about 1.0K.

1. Throttling by default.
2. Access document.body.scrollTop, window.innerWidth once.
3. Provide requestAnimationFrame throttle for high performance.
4. Be able to use events like scrollStart (see below) those edge events.

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

Provide throttled version of window or document events, such like scroll, resize, touch and visibilitychange to subscribe, see below.

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:

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

The format of the payload is:

{
    type: <String>, // could be 'scroll', 'resize' ...
    // you need to pass options.enableScrollInfo = true to subscribe to get the following data
    scroll: {
        top: <Number>, // The scroll position, i.g., document.body.scrollTop
        delta: <Number> // The delta of scroll position, it is helpful for scroll direction
    },
    // you need to pass options.enableResizeInfo = true to subscribe to get the following data
    resize: {
        width: <Number>, // The client width
        height: <Number> // The client height
    },
    // you need to pass options.enableTouchInfo = true to subscribe to get the following data
    touch: {
        axisIntention: <String>, // 'x', 'y', or ''.
        startX: <Number>,
        startY: <Number>,
        deltaX: <Number>,
        deltaY: <Number>
    }
}

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.

options.enableTouchInfo = true allows of getting touch information (see above).

eventType could be one of the following:

1. scroll - window.scoll
2. scrollStart - The start of window.scoll
3. scrollEnd - The end of window.scoll
4. resize - window.resize
5. resizeStart - The start window.resize
6. resizeEnd - The end window.resize
7. visibilitychange - document.visibilitychange (IE8 doesn't support)
8. touchmoveStart - The start of window.touchmove
9. touchmoveEnd - The end of window.touchmove
10. touchmove - window.touchmove
11. touchstart - window.touchstart
12. touchend - window.touchend

options.eventOptions: An options object that specifies characteristics about the event listener (if passive event is supported by the browser)

unsubscribe(eventType: String, callback: Function): Void

Unsubscribe to an event listener, we suggest you use subscription.unsubscribe(), because it may accidentally unsubscribe those events having the same eventType and callback, but different throttleRate.

• This library runs full browser test suite using Sauce Labs.

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