54 lines
1.6 KiB
JavaScript
54 lines
1.6 KiB
JavaScript
// Small buffer so that very tiny scrolls don't trigger mobile header switch
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const MOBILE_SCROLL_TOLERANCE = 5;
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export default Ember.Mixin.create({
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_lastScroll: null,
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_bottomHit: 0,
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calculateDirection(offset) {
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// Difference between this scroll and the one before it.
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const delta = Math.floor(offset - this._lastScroll);
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// This is a tiny scroll, so we ignore it.
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if (delta <= MOBILE_SCROLL_TOLERANCE && delta >= -MOBILE_SCROLL_TOLERANCE)
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return;
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// don't calculate when resetting offset (i.e. going to /latest or to next topic in suggested list)
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if (offset === 0) return;
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const prevDirection = this.mobileScrollDirection;
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const currDirection = delta > 0 ? "down" : null;
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const distanceToBottom = Math.floor(
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$("body").height() - offset - $(window).height()
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);
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// Handle Safari top overscroll first
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if (offset < 0) {
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this.set("mobileScrollDirection", null);
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} else if (currDirection !== prevDirection && distanceToBottom > 0) {
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this.set("mobileScrollDirection", currDirection);
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}
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// We store this to compare against it the next time the user scrolls
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this._lastScroll = Math.floor(offset);
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// Not at the bottom yet
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if (distanceToBottom > 0) {
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this._bottomHit = 0;
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return;
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}
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// If the user reaches the very bottom of the topic, we only want to reset
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// this scroll direction after a second scrolldown. This is a nicer event
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// similar to what Safari and Chrome do.
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Ember.run.debounce(() => {
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this._bottomHit = 1;
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}, 1000);
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if (this._bottomHit === 1) {
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this.set("mobileScrollDirection", null);
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}
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}
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});
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