引用了就报错guard is not a function 请问什么原因

[rocing]

TypeError: guard is not a function
at routeEnterGuard (vue-router.esm.js:2120:12)
at iterator (vue-router.esm.js:1960:7)
at step (vue-router.esm.js:1734:9)
at runQueue (vue-router.esm.js:1742:3)
at eval (vue-router.esm.js:1996:5)
at step (vue-router.esm.js:1731:7)
at eval (vue-router.esm.js:1735:11)
at eval (vue-router.esm.js:1981:11)
at eval (vue-router.esm.js:1809:22)
at iterator (vue-router.esm.js:1960:7)
at step (vue-router.esm.js:1734:9)
at step (vue-router.esm.js:1738:9)
at runQueue (vue-router.esm.js:1742:3)
at HTML5History.confirmTransition (vue-router.esm.js:1989:3)
at HTML5History.transitionTo (vue-router.esm.js:1891:8)
at VueRouter.init (vue-router.esm.js:2542:13)