Don't use ES2015 syntax to allow Babel removal

.eslintignore

@@ -1,2 +1,3 @@
 /node_modules
 /dist
+/tests

.eslintrc.js

@@ -3,6 +3,9 @@ module.exports = {
   env: {
     node: true
   },
+  "plugins": [
+    "no-es2015"
+  ],
   extends: [
     'plugin:vue/recommended',
     'eslint:recommended'
@@ -14,6 +17,8 @@ module.exports = {
     "semi": "error",
     "no-trailing-spaces": "error",
     "comma-dangle": ["error", "never"],
+    "quotes": ["error", "single"],
+    "no-template-curly-in-string": "error",
     "vue/max-attributes-per-line": ["error", { "singleline": 3 }],
     "vue/html-closing-bracket-newline": "error",
     "vue/html-closing-bracket-spacing": "error",
@@ -24,7 +29,7 @@ module.exports = {
         "MethodDefinition": true,
         "ClassDeclaration": true,
         "ArrowFunctionExpression": false,
-        "FunctionExpression": true
+        "FunctionExpression": false
       }
     }],
     "valid-jsdoc": ["error", {
@@ -59,6 +64,26 @@ module.exports = {
         "String": "string"
       }
     }],
+
+    // Don't use ES2015 at all, so we don't need a transpiler like Babel.
+    // This reduces the bundle size dramatically.
+    "no-es2015/no-object-computed-properties": "error",
+    "no-es2015/no-object-shorthand-properties": "error",
+    "no-es2015/no-object-shorthand-method": "error",
+    "no-es2015/only-var": "error",
+    "no-es2015/no-destructuring-assignment": "error",
+    "no-es2015/no-destructuring-params": "error",
+    "no-es2015/no-class": "error",
+    "no-es2015/no-default-params": "error",
+    "no-es2015/no-spread-element": "error",
+    "no-es2015/no-rest-params": "error",
+    "no-es2015/no-generator-function": "error",
+    "no-es2015/no-arrow-func": "error",
+    "no-es2015/no-for-of": "error",
+    "no-es2015/no-template-string": "error",
+
+    // using import is allowed, since webpack gets rid of it automatically
+    "no-es2015/no-import": "off"
   },
   parserOptions: {
     parser: 'babel-eslint'

package.json

@@ -43,6 +43,7 @@
     "@vue/cli-service": "^3.0.0-rc.10",
     "@vue/test-utils": "^1.0.0-beta.20",
     "chai": "^4.1.2",
+    "eslint-plugin-no-es2015": "^1.2.0",
     "node-sass": "^4.9.2",
     "raw-loader": "^0.5.1",
     "sass-loader": "^7.1.0",

src/components/EmbettyEmbed.vue

@@ -14,7 +14,7 @@ export default {
   /**
    * @returns {!object} Component's data.
    */
-  data() {
+  data: function() {
     return {
       embettyLogo: EMBETTY_LOGO,
 
@@ -27,20 +27,20 @@ export default {
      * Override this in child components!
      * @returns {string | undefined} The URL to query for data in this component.
      */
-    url() {
+    url: function() {
       return undefined;
     },
 
     /**
      * @returns {!string} The server URL, either from this component's prop or the global config.
      */
-    _serverUrl() {
+    _serverUrl: function() {
       if (this.serverUrl) {
         return this.serverUrl;
       }
 
       if (!this._embettyVueOptions.serverUrl) {
-        throw new Error(`serverUrl is neither set directly on the ${this.$vnode.tag} component nor globally.`);
+        throw new Error('serverUrl is neither set directly on the ' + this.$vnode.tag + ' component nor globally.');
       }
 
       return this._embettyVueOptions.serverUrl;
@@ -52,7 +52,7 @@ export default {
       /**
        * @param {?string} url The newly set URL.
        */
-      handler(url) {
+      handler: function(url) {
         if (url) {
           this.fetchData();
         }
@@ -63,21 +63,24 @@ export default {
     /**
      * Calls the API of embetty-server using the url set in the calling (child) component.
      */
-    fetchData() {
+    fetchData: function() {
+      var thisCmp = this;
       window.fetch(this.url)
-        .then(response => response.json())
-        .then(data => {
-          this.data = data;
-          this.fetched = true;
+        .then(function (response) {
+          return response.json();
+        })
+        .then(function (data) {
+          thisCmp.data = data;
+          thisCmp.fetched = true;
         });
     },
 
     /**
      * @param {?string} apiEndpoint The API endpoint of the embetty-server.
      * @returns {?string} The given URL, prepended with the embetty-server base URL.
      */
-    _api(apiEndpoint) {
-      return apiEndpoint ? `${this._serverUrl}${apiEndpoint}` : undefined;
+    _api: function(apiEndpoint) {
+      return apiEndpoint ? (this._serverUrl + apiEndpoint) : undefined;
     }
   }
 };