Why is Tether written to the end of the file when compiling app.js Webpack?

Question

Node.js

....
 "devDependencies": {
    "jquery": "^3.2.1",
    "axios": "^0.15.3",
    "cross-env": "^3.2.3",
    "laravel-mix": "0.*",
    "lodash": "^4.17.4",
    "vue": "^2.4.3"
  },
  "dependencies": {
    "tether": "^1.4.0",
    "bootstrap-v4-dev": "^4.0.0-alpha.6",
    "font-awesome": "^4.7.0",
    "jquery-ui": "^1.12.1"
  }
...

window._ = require('lodash');
window.$ = window.jQuery = require('jquery');
require('tether');
window.Vue = require('vue');
window.Bus = new Vue();
window.axios = require('axios');
window.axios.defaults.headers.common = {
    'X-CSRF-TOKEN': window.Laravel.csrfToken,
    'X-Requested-With': 'XMLHttpRequest'
};
require('bootstrap-v4-dev/dist/js/bootstrap');

When I check the app.js file, Tether is always lower, how much?
Because of this, Bootstrap throws errors.