vue实现中部导航栏布局功能

private fixedFlag: boolean = false;
 private unFixedFlag: boolean = true;
 private mounted() {
  window.addEventListener("scroll", this.handleScroll);
 }
 private handleScroll() {
  const scrollTop =
   window.pageYOffset ||
   document.documentElement.scrollTop ||
   document.body.scrollTop;
  if (scrollTop > 300) {
   if (!this.fixedFlag) {
    const obj = document!.getElementById("index-menu");
    const obj2 = document!.getElementById("fake-area");
    obj!.style.position = "fixed";
    obj!.style.top = "77px";
    obj2!.style.position = "fixed";
    obj2!.style.top = "47px";
    this.fixedFlag = true;
    this.unFixedFlag = false;
   }
  } else {
   if (!this.unFixedFlag) {
    const obj = document!.getElementById("index-menu");
    const obj2 = document!.getElementById("fake-area");
    obj!.style.position = "";
    obj!.style.top = "";
    obj2!.style.position = "";
    obj2!.style.top = "";
    this.unFixedFlag = true;
    this.fixedFlag = false;
   }
  }
 }