JS入门开发者编写随机名言生成器出现数组元素为undefined问题求助

安全阿岳

2026-9-28

问题根因

计算随机索引的代码行中，数组长度属性名拼写错误，将正确的length错写为lenth，缺失了字母g。
由于不存在quotes.lenth属性，读取该属性会得到undefined，代入随机数运算后得到NaN，用非法下标访问数组最终返回undefined。

修复方法

仅需修改点击事件监听内的属性拼写即可，修改后的完整JS代码如下：

let btn = document.getElementById("btn");
let output = document.getElementById("output");
let quotes = [
  "The greatest glory in living lies not in never falling, but in rising every time we   fall. -Nelson Mandela",
  "The way to get started is to quit talking and begin doing. -Walt Disney",
  "Your time is limited, so don't waste it living someone else's life. Don't be trapped by dogma – which is living with the results of other people's thinking. -Steve Jobs",
  "If life were predictable it would cease to be life, and be without flavor. -Eleanor Roosevelt",
  "If you look at what you have in life, you'll always have more. If you look at what you don't have in life, you'll never have enough. -Oprah Winfrey",
  "If you set your goals ridiculously high and it's a failure, you will fail above everyone else's success. -James Cameron",
  "Life is what happens when you're busy making other plans. -John Lennon",
];
btn.addEventListener("click", function() {
  let randomQuote = quotes[Math.floor(Math.random() * quotes.length)];
  output.innerHTML = randomQuote;
});