滚动条不占位置

以Vue + Element Dialog为例，用ResizeObserver监听容器高度变化，当高度大于最大高度（出现滚动条），右边距减去滚动条的宽度，反之恢复正常边距

<el-dialog>
  <div class="dialog_body" v-fix-scroll-bar="this">
    <slot />
  div>
el-dialog>

export default {
  data() {
    return {
      resizeObserver: null,
    }
  },

  methods: {
    setScrollBar() {
      this.resizeObserver = new ResizeObserver((entries) => {
        for (let entry of entries) {
          const cr = entry.contentRect;

          const el_dialog_body = entry.target.parentNode;
          const maxHeight = window.getComputedStyle(el_dialog_body).maxHeight;

          if (maxHeight && cr.height > parseInt(maxHeight)) {
            el_dialog_body.style.paddingRight = "20px";
          } else {
            el_dialog_body.style.paddingRight = "32px";
          }
        }
      });
    },
  },

  mounted() {
    this.setScrollBar();
  },

  directives: {
    fixScrollBar: {
      inserted: (el, binding) => {
        const _this = binding.value;
        _this.resizeObserver.observe(el);
      },
      unbind: (el, binding) => {
        const _this = binding.value;
        _this.resizeObserver.unobserve(el);
      },
    },
  },
}