<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8">
    <title>替换文本框内容</title>
  </head>
  <body>
    <input type="text" id="input1" placeholder="输入框1">
    <input type="text" id="input2" placeholder="输入框2">
    <input type="text" id="input3" placeholder="输入框3">

    <button onclick="replace()">替换内容</button>

    <script>
      function replace() {
        var input1 = document.getElementById("input1").value;
        var input2 = document.getElementById("input2").value;
        var input3 = document.getElementById("input3");

        // 将输入框1中的特殊字符进行转义
        var regex = new RegExp(input1.replace(/[.*+?^${}()|[\]\\]/g, '\\$&'), 'g');

        var text = input3.value;
        text = text.replace(regex, input2);
        input3.value = text;
      }
    </script>
  </body>
</html>