Uncaught SyntaxError: Identifier [VARIABLE_NAME] has already been declared の解決法

Uncaught Error: Module build failed (from ./node_modules/babel-loader/lib/index.js):
SyntaxError: /Users/hoge/piyo/dir_name/src/bld_dir/assets/js/_common/asyncTransition/AsyncTransition.js: Identifier 'VARIABLE_NAME' has already been declared.

// *--before
    page.exit((context, next) => {
      var hash, pageY;
      const hash = location.hash;
      const pageY = window.scrollY || window.pageYOffset;
      history.replaceState({
        path: location.pathname + hash,
        pageY
      }, document.title, location.pathname + hash);
      next();
    });
    this._initPageRouting();
  }

// *--after
    page.exit((context, next) => {
      // var hash, pageY;
      const hash = location.hash;
      const pageY = window.scrollY || window.pageYOffset;
      history.replaceState({
        path: location.pathname + hash,
        pageY
      }, document.title, location.pathname + hash);
      next();
    });
    this._initPageRouting();
  }