Javascript 检查高度是否已从一定量更改

我想检查一个数字是否从另一个数字增加或减少到某个数字

例如：

Let a = 20;
Let b = 20; 

如果

b

比

a

增加了5，则返回

true

如果

b

比

a

减少了5，则返回

true

提前谢谢你的帮助

var lastHeightSize = document.body.scrollHeight;

function checkBodySizeChange () {
    // instead of checking if lastHeightSize is not equal to document.body.scrollheight,
    // check if document.body.scrollheight has increased or decreased by 20
    const heightChanged = lastHeightSize !== document.body.scrollHeight;
    if (heightChanged) {
        trigger(document.body, 'sizechange');
        lastHeightSize = document.body.scrollHeight;
    }
    window.requestAnimationFrame(checkBodySizeChange);
}

使用

---

然后你就可以看到它的正负变化量了

以下是反映rlemons答案的更新代码

  var lastHeightSize = document.body.scrollHeight;
  function checkBodySizeChange () {
    const heightChanged = Math.abs(lastHeightSize - document.body.scrollHeight) > 120;
    if (heightChanged) {
      trigger(document.body, 'sizechange');
      lastHeightSize = document.body.scrollHeight;
    }
    window.requestAnimationFrame(checkBodySizeChange);
  }

---

Math.abs（oldV-newV）>changedLimit

！非常感谢您的快速回复！我加上它作为答案。试图摆脱在评论中回答的习惯：P

  var lastHeightSize = document.body.scrollHeight;
  function checkBodySizeChange () {
    const heightChanged = Math.abs(lastHeightSize - document.body.scrollHeight) > 120;
    if (heightChanged) {
      trigger(document.body, 'sizechange');
      lastHeightSize = document.body.scrollHeight;
    }
    window.requestAnimationFrame(checkBodySizeChange);
  }