Question

这是我在控制台中收到错误的一段代码，有人能指出我做错了吗？提前谢谢。

var intervalID = setInterval(function() {
    // every 4 seconds execute following
    var visibleWord = document.getElementsByClassName('visible')[0],
    nextWord = visibleWord.nextSibling;

    // check if nextSibling is textnode (whitespace) - if so get next next sibling. 
    if (nextWord.nodeType == 3) nextWord = nextWord.nextSibling;

    // if there is a next node 
    if (!(nextWord == null)) {
        visibleWord.setAttribute('class', 'hidden');
        nextWord.setAttribute('class', 'visible');
    } else {
        clearInterval(intervalID);
    }
}, 4000)

Answer 1

错误意味着在运行代码时，您要查找的元素（使用类visible）不存在。也许你过早地运行代码（在解析DOM之前）。

尝试添加简单的if条件：

var visibleWord = document.getElementsByClassName('visible')[0];

if (!visibleWord) {
    return;
}

// continue with the code... 
var nextWord = visibleWord.nextSibling;

Answer 2

表示没有visibleWord所以如果是这样的话，你可以这样返回：

var intervalID = setInterval(function() {
// every 4 seconds execute following
var visibleWord = document.getElementsByClassName('visible')[0],
    if(null == visibleWord) {    // added this line
        return;                  // and this line
    }                            // and this line
    nextWord = visibleWord.nextSibling;
// check if nextSibling is textnode (whitespace) - if so get next next sibling. 
if (nextWord.nodeType == 3) nextWord = nextWord.nextSibling;
// if there is a next node 
if (!(nextWord == null)) {
    visibleWord.setAttribute('class', 'hidden');
    nextWord.setAttribute('class', 'visible');
} else {
    clearInterval(intervalID);
}
}, 4000)

未捕获的TypeError：无法读取属性＆＃39; nextSibling＆＃39;未定义的

2 个答案: