SOURCE

    $(function () {
        $(".js-convert").click(function () {
            var str = $("#pre").val();
            var resultStr =  str.replace(/\[[^\]]*]/g,'').replace(/ /g,'').replace(/。/g, '。\r\n');
            $("#result").val(resultStr);
        });
    });

<div class="container">
  <textarea class="text-container" id="pre">
  </textarea>
    <div class="button-container">
              <button class="js-convert">
            去掉中括号
        </button>
    </div>
    <textarea class="text-container" id="result">
  </textarea>
</div>

.text-container {
  width: 300px;
  height: 500px;
  float: left;
}

.button-container {
  height: 500px;
  float: left;
  flex-direction: column;
  display: flex;
  align-items: center;
  justify-content: center;
}

.button-container button{
  margin:10px 10px;
  font-size:16px;
}