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// Copyright 2022 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
export class ViewElements {
container: HTMLElement;
scrollTop: number;
constructor(container: HTMLElement) {
this.container = container;
this.scrollTop = undefined;
}
public consider(element: HTMLElement, doConsider: boolean): void {
if (!doConsider) return;
const newScrollTop = this.computeScrollTop(element);
if (isNaN(newScrollTop)) {
console.warn("New scroll top value is NaN");
}
if (this.scrollTop === undefined) {
this.scrollTop = newScrollTop;
} else {
this.scrollTop = Math.min(this.scrollTop, newScrollTop);
}
}
public apply(doApply: boolean): void {
if (!doApply || this.scrollTop === undefined) return;
this.container.scrollTop = this.scrollTop;
}
private computeScrollTop(element: HTMLElement): number {
const height = this.container.offsetHeight;
const margin = Math.floor(height / 4);
const pos = element.offsetTop;
const currentScrollTop = this.container.scrollTop;
if (pos < currentScrollTop + margin) {
return Math.max(0, pos - margin);
} else if (pos > (currentScrollTop + 3 * margin)) {
return Math.max(0, pos - 3 * margin);
}
return currentScrollTop;
}
}
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