<pre class="shiki github-dark shaku"><code>/** * @param {Element} root * @param {Element} target * @return {Elemnt | null} */function previousLeftSibling(root, target) { if (!root) return null; let queue = [root]; while (queue.length) { let len = queue.length; let prev = null; for (let i = 0; i &lt; len; i++) { let node = queue.shift(); //如果找到和target一样的node, 那么返回prev node if (node === target) return prev; for (let child of node.children) { queue.push(child); } prev = node; // update prev here } }}</code></pre>

中文解释- BFS

Given a DOM tree and a target element, please return the previous left sibling. [https://cdn.bfe.dev/bfe/img/2a737BvrqUaK1F9YnxrD1JkYV58y8Le8_1063x546…