src/Placement.js
/**
         * When element is in view per viewability constants (50% for 1s) trigger handler once
         * @param element
         * @param handler
         * @private
         */
When element is in view per viewability constants (50% for 1s) trigger handler once
@param element
@param handler
@private
When element is in view per viewability constants ( 50% for 1s ) trigger handler once @param element @param handler @private
_addOnceViewedHandler(element, handler) {
            let controller = {
                element,
                successfulCount: 0,
                handler
            };
            this._viewedWatchers.push(controller);
            this._toggleViewWatcher(true);
        }
_addOnceViewedHandler ( element , handler ) { let controller = { element , successfulCount : 0 , handler } ; this . _viewedWatchers . push ( controller ) ; this . _toggleViewWatcher ( true ) ; }
When element is in view per viewability constants (50% for 1s) trigger handler once
 @param element
 @param handler
 @private
When element is in view per viewability constants ( 50% for 1s ) trigger handler once @param element @param handler @private
// Add our element to the watch list and turn on the watcher if not already on