50 lines
1.9 KiB
TypeScript
50 lines
1.9 KiB
TypeScript
export class StickySidebar {
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private lastScrollTop = 0;
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private container: HTMLElement;
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private el: HTMLElement;
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private spacer: HTMLElement;
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private marginTop: number;
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private isTop = false;
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private isBottom = false;
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private offsetTop: number;
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private globalHeaderHeight: number = 59;
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constructor(container: StickySidebar['container'], marginTop = 0, globalHeaderHeight = 0) {
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this.container = container;
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this.el = this.container.children[0] as HTMLElement;
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this.el.style.position = 'sticky';
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this.spacer = document.createElement('div');
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this.container.prepend(this.spacer);
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this.marginTop = marginTop;
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this.offsetTop = this.container.getBoundingClientRect().top;
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this.globalHeaderHeight = globalHeaderHeight;
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}
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public calc(scrollTop: number) {
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if (scrollTop > this.lastScrollTop) { // downscroll
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const overflow = Math.max(0, this.globalHeaderHeight + (this.el.clientHeight + this.marginTop) - window.innerHeight);
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this.el.style.bottom = null;
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this.el.style.top = `${-overflow + this.marginTop + this.globalHeaderHeight}px`;
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this.isBottom = (scrollTop + window.innerHeight) >= (this.el.offsetTop + this.el.clientHeight);
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if (this.isTop) {
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this.isTop = false;
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this.spacer.style.marginTop = `${Math.max(0, this.globalHeaderHeight + this.lastScrollTop + this.marginTop - this.offsetTop)}px`;
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}
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} else { // upscroll
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const overflow = this.globalHeaderHeight + (this.el.clientHeight + this.marginTop) - window.innerHeight;
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this.el.style.top = null;
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this.el.style.bottom = `${-overflow}px`;
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this.isTop = scrollTop + this.marginTop + this.globalHeaderHeight <= this.el.offsetTop;
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if (this.isBottom) {
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this.isBottom = false;
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this.spacer.style.marginTop = `${this.globalHeaderHeight + this.lastScrollTop + this.marginTop - this.offsetTop - overflow}px`;
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}
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}
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this.lastScrollTop = scrollTop <= 0 ? 0 : scrollTop;
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}
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}
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