javascript - 如何对强制回流的 Javascript 操作进行分组？

Question

我有一个项目负责管理元素的渲染，但我遇到了替换元素然后专注于之前关注的任何内容的性能问题。

下面是一个复制性能问题的最小示例:

const renderPage = () => {
  // get the old section element
  const oldSection = document.querySelector('section')

  // create a new section element (we'll replaceWith later)
  const newSection = document.createElement('section')
  
  // create the render button
  const newButton = document.createElement('button')
  newButton.innerHTML = 'Render Page'
  newButton.onclick = renderPage
  newSection.appendChild(newButton)
  
  // create a bunch of elements
  const dummyDivs = [...new Array(100000)].forEach(() => {
    const dummy = document.createElement('div')
    dummy.innerHTML = 'dummy'
    newSection.appendChild(dummy)
  })
  
  // replace the old page with the new one (causes forced reflow)
  oldSection.replaceWith(newSection)
  // reattach focus on the button (causes forced reflow)
  newButton.focus()
}

window.renderPage = renderPage

<section>
  <button onclick="renderPage()">Render</button>
</section>

在本地运行时，我在 Chrome/Edge 的性能报告中看到以下内容

replaceWith 和 focus 都会触发强制重排。有没有办法对这些操作进行批处理或分组，以便只发生一次回流？我意识到根本没有办法真正解决这种情况，但如果我可以对它们进行批处理，我认为这可能会提高我的性能。

Answer 1

事实上，焦点总是导致回流:What forces layout / reflow

所以你可以做的是通过独立插入新按钮来减少回流时间，启动焦点，然后你可以附加其他 child :

工作示例:Example

const renderPage = () => {
  // get the old section element
  const oldSection = document.querySelector('section')

  // create a new section element (we'll replaceWith later)
  const newSection = document.createElement('section')
  
  // create the render button
  const newButton = document.createElement('button')
  newButton.innerHTML = 'Render Page'
  newButton.onclick = renderPage
  newSection.appendChild(newButton)
  
  // create a bunch of elements
  const dummies = []; //  store in seperate array
  const dummyDivs = [...new Array(100000)].forEach(() => {
    const dummy = document.createElement('div')
    dummy.innerHTML = 'dummy';
    dummies.push(dummy)
  })
  //  insert new section only with new button
  oldSection.replaceWith(newSection)
  newButton.focus(); // always causes reflow; but fast because it's only one element
  //  store all other nodes after focus
  newSection.append(...dummies)
}

window.renderPage = renderPage