hasn"t mint-ui been globally introduced in main.js and installed with Vue.use (meaning that toast is not also installed? ), but why do you use toast to report to undefined, directly? Is there a scope problem?
main.js
import Vue from "vue"
import MintUI from" mint-ui"
import "mint-ui/lib/style.css"
Vue.use (MintUI)
new Vue ({
created(){
new Toast("hello"); //toast is undefined
}
})