100vw가 수평 스크롤바를 일으키는 이유

This post is from my personal blog here

* {
  border: 1px solid red;
}

var docWidth = document.documentElement.offsetWidth;

[].forEach.call(document.querySelectorAll('*'), function (el) {
  if (el.offsetWidth > docWidth) {
    console.log(el);
  }
});

When you set an element's width to 100vw, the element's width now will be the whole view width of the browser and the important part is 100vw does not include the vertical scrollbar's width into its calculation at all. Therefore, when there is a vertical scrollbar, the total width will be the sum of the element's width and the vertical scrollbar's width, which causes the overflow on the x-axis and thus the horizontal scrollbar.