JavaScript

    var an =  document.getElementById('按钮元素id');
    
    var tee = document.getElementById('要显示或的元素id');
//这里设置元素默认隐藏
    tee.style.display = 'none';

    an.onclick = function () {
          if (tee.style.display == 'block') {
            tee.style.display = 'none';
            an.innerHTML = "≡";
          } else {
            tee.style.display = 'block';
            an.innerHTML = "X";
          };
        };

html示例

screenshots.gif

<!DOCTYPE html>
<html lang="zh">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>网页名称</title>
  <style>


  </style>
</head>
<body>
  
    <a id="t">X</a>
    <h1 id="o">1111111111111111111111111111111</h1>


  <script>
    var an =  document.getElementById('t');
    
    var tee = document.getElementById('o');

    tee.style.display = 'none';

    an.onclick = function () {
          if (tee.style.display == 'block') {
            tee.style.display = 'none';
            an.innerHTML = "≡";
          } else {
            tee.style.display = 'block';
            an.innerHTML = "X";
          };
        };

  </script>
</body>