查看器的大小调整

要为查看器添加大小调整功能，可以使用以下代码示例：

1. HTML 结构：

<div id="viewer" style="width: 400px; height: 300px; border: 1px solid #ccc; overflow: auto;">
  <!-- 查看器内容 -->
</div>
<button id="increaseBtn">增加大小</button>
<button id="decreaseBtn">减小大小</button>

2. JavaScript 代码：

var viewer = document.getElementById("viewer");
var increaseBtn = document.getElementById("increaseBtn");
var decreaseBtn = document.getElementById("decreaseBtn");

increaseBtn.addEventListener("click", function() {
  var currentWidth = viewer.offsetWidth;
  var currentHeight = viewer.offsetHeight;
  viewer.style.width = (currentWidth + 50) + "px";
  viewer.style.height = (currentHeight + 50) + "px";
});

decreaseBtn.addEventListener("click", function() {
  var currentWidth = viewer.offsetWidth;
  var currentHeight = viewer.offsetHeight;
  viewer.style.width = (currentWidth - 50) + "px";
  viewer.style.height = (currentHeight - 50) + "px";
});

以上代码将为查看器添加两个按钮，分别用于增加和减小大小。点击增加按钮后，查看器的宽度和高度将增加 50 像素；点击减小按钮后，查看器的宽度和高度将减小 50 像素。可以根据需要修改按钮的样式和调整大小的增量。