devdocs/assets/javascripts/views/list/list_select.js

app.views.ListSelect = class ListSelect extends app.View {
  static activeClass = "active";

  static events = { click: "onClick" };

  deactivate() {
    if (super.deactivate(...arguments)) {
      this.deselect();
    }
  }

  select(el) {
    this.deselect();
    if (el) {
      el.classList.add(this.constructor.activeClass);
      $.trigger(el, "select");
    }
  }

  deselect() {
    let selection;
    if ((selection = this.getSelection())) {
      selection.classList.remove(this.constructor.activeClass);
      $.trigger(selection, "deselect");
    }
  }

  selectByHref(href) {
    if (this.getSelection()?.getAttribute("href") !== href) {
      this.select(this.find(`a[href='${href}']`));
    }
  }

  selectCurrent() {
    this.selectByHref(location.pathname + location.hash);
  }

  getSelection() {
    return this.findByClass(this.constructor.activeClass);
  }

  onClick(event) {
    if (event.which !== 1 || event.metaKey || event.ctrlKey) {
      return;
    }
    const target = $.eventTarget(event);
    if (target.tagName === "A") {
      this.select(target);
    }
  }
};