javascript - 如何等待 javascript 中出现元素？

Question

(function() {
    document.evaluate('/html/body/nav/section[4]/div/form[1]/input[4]', document, null, XPathResult.FIRST_ORDERED_NODE_TYPE, null).singleNodeValue.click();
    Sleep(15);
    window.close();
})();

所以点击功能可以工作，但是一旦我添加 sleep windows.close 就不再工作了？我还在学习 Javascript，有人可以帮忙吗？我想做的就是让它单击“投票”按钮，然后关闭事件选项卡。

Answer 1

尝试这个函数，它将在元素存在时等待。

function waitWhileElementPresent(cssLocator, timeoutInSeconds) {
    var currentTime = new Date().getTime();
    var endTime = currentTime + timeoutInSeconds * 1000;
    var checkExist = setInterval(function () {
        if (document.querySelectorAll(cssLocator).length == 0) {
            clearInterval(checkExist);
            console.log('waited until element not present.');
            return;
        } else if (endTime < new Date().getTime()) {
            clearInterval(checkExist);
            console.log('element still found after ' + timeoutInSeconds + ' seconds.');
            return;
        } else { 
            console.log('waiting for element not present ...'); 
        } 
    }, 100);
}

这是另一个函数，它将等待元素出现

function waitUntilElementPresent(cssLocator, timeoutInSeconds) {
    var currentTime = new Date().getTime();
    var endTime = currentTime + timeoutInSeconds * 1000;
    var checkExist = setInterval(function () {
        if (document.querySelectorAll(cssLocator).length) {
            clearInterval(checkExist);
            return;
        } else if (endTime < new Date().getTime()) {
            clearInterval(checkExist);
            console.log('not found in specified time.');
            return;
        } else {
            console.log('waiting for element to be present…');
        } 
    }, 100); 
}