基于复选框活动启用/禁用输入[重复]

您的脚本在加载HTML之前执行,因此找不到任何内容:

document.getElementById('average_price')

将脚本移动到页面底部,传统上只在 </body> 标签。

通过编程禁用输入

提醒:始终将脚本放在结束正文标记之前

HTML

<h2>Generate Custom Report</h2>
  <br>
  <input type="checkbox" id="average_price" name="average_price"> <b>Average Price</b>
  <br>
  <input type="text" id="average_price_symbol" name="average_price_symbol" placeholder="symbol" >
  <br>
  <input type="submit" value="RUN">

JS

var checkbox = document.getElementById('average_price');
var input = document.getElementById('average_price_symbol');

input.disabled = true;
checkbox.addEventListener('change', function (e) {
  console.log('CHECKED', this.checked);
  input.disabled = !this.checked;
  (!input.disabled && input.focus());
});

将代码添加到文档就绪函数将有所帮助。

$('document').ready(function(){ document.getElementById('average_price') });