the vue project I built through vue-cli3 selected the module that supports ts, and then wrote a public js file today. The error report is not declared when it is introduced with import in main.js, but it can be used. The error message is as follows:

21:23 Could not find a declaration file for module "./libs/commonFun.js". "E:///internal-recommended/src/libs/commonFun.js" implicitly has an "any" type.
    19 | Vue.config.devtools = true;
    20 | // js
  > 21 | import commonFun from "./libs/commonFun.js";
       |                       ^
    22 | Vue.prototype.commonFun = commonFun;
    23 |
    24 | new Vue({
Version: typescript 3.1.6

main.js introduction code is as follows

// js
import commonFun from "./libs/commonFun.js";
Vue.prototype.commonFun = commonFun;

commonFun.js is as follows

import {
    MessageBox
} from "element-ui";
export default {
    showConfirm(option) {
        MessageBox.confirm(option.confirmtxt, "", {
            confirmButtonText: option.confirmoktxt,
            cancelButtonText: option.confirmcanceltxt,
            type: "warning",
            center: true
        }).then(() => {
            option.success()
        }).catch(() => {
            console.log("")
        });
    }
}

because I used ts for the first time, I did not find the declaration of this kind of introduction file in the official document, and Baidu did not find the relevant information. I also asked the boss who thought no to help me to express my thanks.