Nexus.Reader/src/NexusReader.UI.Shared/wwwroot/js/viewport.js

/**
 * Viewport and scrolling utilities for NexusReader.
 * Avoids eval() usage, supports CSP, AOT-safety, and prevents memory leaks.
 */

export function isMobileViewport() {
    return window.innerWidth < 768;
}

export function registerViewportObserver(dotNetHelper) {
    let currentIsMobile = window.innerWidth < 768;
    
    const listener = () => {
        const isMobile = window.innerWidth < 768;
        if (isMobile !== currentIsMobile) {
            currentIsMobile = isMobile;
            dotNetHelper.invokeMethodAsync('OnViewportChanged', isMobile);
        }
    };

    // Store listener directly on the JS object wrapper of the DotNetObjectReference for elegant cleanup
    dotNetHelper._viewportListener = listener;
    window.addEventListener('resize', listener);
}

export function unregisterViewportObserver(dotNetHelper) {
    if (dotNetHelper && dotNetHelper._viewportListener) {
        window.removeEventListener('resize', dotNetHelper._viewportListener);
        delete dotNetHelper._viewportListener;
    }
}

export function scrollIntoView(id) {
    const el = document.getElementById(id);
    if (el) {
        el.scrollIntoView({ behavior: 'smooth', block: 'center' });
        return true;
    }
    return false;
}

// NOTE: Assumes the selector matches the active scroll container (default '.reader-canvas').
// Scoping is flexible to avoid issues if SSR pre-render or animated layouts render multiple wrappers.
export function scrollToTop(selector = '.reader-canvas') {
    const el = document.querySelector(selector);
    if (el) {
        el.scrollTop = 0;
        return true;
    }
    return false;
}