获取添加的DOM节点的className（mutationObserver） [英] getting the className of added DOM node (mutationObserver)

问题描述

我正在编写一个简单的用户脚本，如果其中包含某些单词列表，它将自动隐藏Facebook帖子。核心功能有效，但是我的 MutationObserver 似乎没有读取突变的 className .addedNodes 正确。我遍历 mutation.addedNodes 并检查其中任何一个元素是否具有类 userContentWrapper ，但是该测试的结果始终为false －即使元素确实具有类。

I'm writing a simple userscript that will auto-hide a Facebook post if it contains a certain list of words. The core functionality works, but my MutationObserver doesn't seem to read the className of mutation.addedNodes properly. I loop through mutation.addedNodes and check if any of those elements have the class userContentWrapper, but the result of that test is always false -- even if the element does have the class.

var startObserver = function() {        
    var observer = new MutationObserver(function(mutations) {        
        mutations.forEach(function(mutation) {            
            var added = mutation.addedNodes;            
            for (var i = 0; i < added.length; i++) {                
                if (/\buserContentWrapper\b/.test(added[i].className)) {
                    processFilter(added[i]);
                }
            }
        });        
    });    
    var obj = {childList: true, subtree: true, attributes: true};
    observer.observe(document.documentElement, obj);
};

我只能假设观察者正在分析添加的节点，直到它完全具有地点。如何让观察者等待处理节点，直到节点完全完成？还是我不理解这个问题？

I can only assume that the observer is analyzing the added node before it's fully formed with all the attributes in place. How can I make the observer wait to process the node until it's fully complete? Or am I not understanding the problem?

预先感谢...

推荐答案

一些添加的节点是容器，因此您应该检查它们的内部：

Some of the added nodes are containers so you should check their insides:

const observer = new MutationObserver(onMutation);
observer.observe(document, {
  childList: true,
  subtree: true,
});

function onMutation(mutations) {
  const found = [];
  for (const { addedNodes } of mutations) {
    for (const node of addedNodes) {
      if (!node.tagName) continue; // not an element
      if (node.classList.contains('userContentWrapper')) {
        found.push(node);
      } else if (node.firstElementChild) {
        found.push(...node.getElementsByClassName('userContentWrapper'));
      }
    }
  }
  found.forEach(processFilter);
}

MutationObserver回调是作为阻止DOM和JS引擎的微任务执行的，因此尝试使其速度更快，尤其是如果它运行在生成大量DOM突变的复杂网站（例如facebook）上时。可以在devtools（ F12 键）事件探查器/时间轴面板中进行测试。

MutationObserver callback is executed as a microtask that blocks DOM and JS engine so try to make it fast, especially if it runs on a complex site such as facebook that generates lots of DOM mutations. This can be tested in devtools (F12 key) profiler/timeline panels.

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