这里有一个用Javascript编写的promise返回解决方案(没有混乱的回调)。默认情况下，它每200ms检查一次。

function waitFor(selector) {
    return new Promise(function (res, rej) {
        waitForElementToDisplay(selector, 200);
        function waitForElementToDisplay(selector, time) {
            if (document.querySelector(selector) != null) {
                res(document.querySelector(selector));
            }
            else {
                setTimeout(function () {
                    waitForElementToDisplay(selector, time);
                }, time);
            }
        }
    });
}

下面是一个函数，充当MutationObserver的薄包装器。唯一的要求是浏览器支持MutationObserver;不依赖于JQuery。运行下面的代码片段以查看一个工作示例。

function waitForMutation(parentNode, isMatchFunc, handlerFunc, observeSubtree, disconnectAfterMatch) { var defaultIfUndefined = function(val, defaultVal) { return (typeof val === "undefined") ? defaultVal : val; }; observeSubtree = defaultIfUndefined(observeSubtree, false); disconnectAfterMatch = defaultIfUndefined(disconnectAfterMatch, false); var observer = new MutationObserver(function(mutations) { mutations.forEach(function(mutation) { if (mutation.addedNodes) { for (var i = 0; i < mutation.addedNodes.length; i++) { var node = mutation.addedNodes[i]; if (isMatchFunc(node)) { handlerFunc(node); if (disconnectAfterMatch) observer.disconnect(); }; } } }); }); observer.observe(parentNode, { childList: true, attributes: false, characterData: false, subtree: observeSubtree }); } // Example waitForMutation( // parentNode: Root node to observe. If the mutation you're looking for // might not occur directly below parentNode, pass 'true' to the // observeSubtree parameter. document.getElementById("outerContent"), // isMatchFunc: Function to identify a match. If it returns true, // handlerFunc will run. // MutationObserver only fires once per mutation, not once for every node // inside the mutation. If the element we're looking for is a child of // the newly-added element, we need to use something like // node.querySelector() to find it. function(node) { return node.querySelector(".foo") !== null; }, // handlerFunc: Handler. function(node) { var elem = document.createElement("div"); elem.appendChild(document.createTextNode("Added node (" + node.innerText + ")")); document.getElementById("log").appendChild(elem); }, // observeSubtree true, // disconnectAfterMatch: If this is true the hanlerFunc will only run on // the first time that isMatchFunc returns true. If it's false, the handler // will continue to fire on matches. false); // Set up UI. Using JQuery here for convenience. $outerContent = $("#outerContent"); $innerContent = $("#innerContent"); $("#addOuter").on("click", function() { var newNode = $("<div><span class='foo'>Outer</span></div>"); $outerContent.append(newNode); }); $("#addInner").on("click", function() { var newNode = $("<div><span class='foo'>Inner</span></div>"); $innerContent.append(newNode); }); .content { padding: 1em; border: solid 1px black; overflow-y: auto; } #innerContent { height: 100px; } #outerContent { height: 200px; } #log { font-family: Courier; font-size: 10pt; } <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <h2>Create some mutations</h2> <div id="main"> <button id="addOuter">Add outer node</button> <button id="addInner">Add inner node</button> <div class="content" id="outerContent"> <div class="content" id="innerContent"></div> </div> </div> <h2>Log</h2> <div id="log"></div>

你可以这样做

$('#yourelement').ready(function() {

});

请注意，这只在从服务器请求元素时元素出现在DOM中时才有效。如果元素是通过JavaScript动态添加的，那么它将不起作用，您可能需要查看其他答案。

如果可以的话，我会尽量避开突变观察者，所以我想到了这个。它看起来类似于上面的一些其他答案。该函数将查找给定DOM调用中存在的第一个元素——className是预期的用法，但它也可以接受tagName或Id。如果您正在寻找具有给定类名或标记名的元素数量，则还可以为精确索引添加参数。

    async function waitUntilElementExits(domkey,domquery,maxtime){
        const delay = (ms) => new Promise(res => setTimeout(res, ms));
        for(let i=0; i<maxtime; i=i+200){
            await delay(200);
            let elm = document[domkey](domquery);
            if( (domkey == 'getElementById' && elm) || elm?.[0] ) break;
        }
    }
    // usage
    await waitUntilElementExits('getElementByClassName','some_class_name',10000)

更新

下面是一个更新的版本，可以使用承诺。如果达到特定的尝试次数，它也会“停止”。

function _waitForElement(selector, delay = 50, tries = 100) {
    const element = document.querySelector(selector);

    if (!window[`__${selector}`]) {
      window[`__${selector}`] = 0;
      window[`__${selector}__delay`] = delay;
      window[`__${selector}__tries`] = tries;
    }

    function _search() {
      return new Promise((resolve) => {
        window[`__${selector}`]++;
        setTimeout(resolve, window[`__${selector}__delay`]);
      });
    }

    if (element === null) {
      if (window[`__${selector}`] >= window[`__${selector}__tries`]) {
        window[`__${selector}`] = 0;
        return Promise.resolve(null);
      }

      return _search().then(() => _waitForElement(selector));
    } else {
      return Promise.resolve(element);
    }
  }

用法很简单，用await使用它只是确保你在一个 异步功能:

const start = (async () => {
  const $el = await _waitForElement(`.my-selector`);
  console.log($el);
})();

过时的版本

只需添加所需的选择器。一旦找到元素，就可以在回调函数中访问它。

const waitUntilElementExists = (selector, callback) => {
const el = document.querySelector(selector);

if (el){
    return callback(el);
}

setTimeout(() => waitUntilElementExists(selector, callback), 500);
}

waitUntilElementExists('.wait-for-me', (el) => console.log(el));

对于一个使用jQuery的简单方法，我发现这工作得很好:

  // Wait for element to exist.
  function elementLoaded(el, cb) {
    if ($(el).length) {
      // Element is now loaded.
      cb($(el));
    } else {
      // Repeat every 500ms.
      setTimeout(function() {
        elementLoaded(el, cb)
      }, 500);
    }
  };

  elementLoaded('.element-selector', function(el) {
    // Element is ready to use.
    el.click(function() {
      alert("You just clicked a dynamically inserted element");
    });
  });

在这里，我们只需每500毫秒检查一次元素是否加载，当加载成功时，我们就可以使用它。

这对于向已动态添加到文档中的元素添加单击处理程序特别有用。