<pre class="shiki github-dark shaku"><code>/** * @param {HTMLElement | null} root * @return {HTMLElement[]} */function flatten(root) { const result = [] if(!root) return result const queue = [root] while(queue.length&gt;0){ const node = queue.shift() result.push(node) for(let i=0;i&lt;node.children.length;i++){ queue.push(node.children[i]) } } return result}</code></pre>

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Given a DOM tree, flatten it into an one dimensional array, in the order of layer by layer, like below. [https://cdn.bfe.dev/bfe/img/ykqFdOIOaXFyn2uZ8…