chessground/dist/sync.js

lichess.org chess ui

// append and remove only. No updates.
export function syncShapes(shapes, root, renderShape) {
    const hashesInDom = new Map(), // by hash
    toRemove = [];
    for (const sc of shapes)
        hashesInDom.set(sc.hash, false);
    let el = root.firstElementChild, elHash;
    while (el) {
        elHash = el.getAttribute('cgHash');
        // found a shape element that's here to stay
        if (hashesInDom.has(elHash))
            hashesInDom.set(elHash, true);
        // or remove it
        else
            toRemove.push(el);
        el = el.nextElementSibling;
    }
    // remove old shapes
    for (const el of toRemove)
        root.removeChild(el);
    // insert shapes that are not yet in dom
    for (const sc of shapes) {
        if (!hashesInDom.get(sc.hash))
            root.appendChild(renderShape(sc));
    }
}
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