Use const for never redefined variable

frontend/package.json

@@ -8,19 +8,24 @@
     "lint": "vue-cli-service lint"
   },
   "dependencies": {
-    "core-js": "^2.6.5",
+    "core-js": "^3.6.4",
     "vue": "^2.6.10",
     "vue-router": "^3.0.3",
-    "vue-shortkey": "^3.1.7"
+    "vue-shortkey": "^3.1.7",
+    "webpack": "^4.41.6"
   },
   "devDependencies": {
-    "@vue/cli-plugin-babel": "^3.8.0",
-    "@vue/cli-plugin-eslint": "^3.8.0",
-    "@vue/cli-service": "^3.8.0",
-    "@vue/eslint-config-standard": "^4.0.0",
+    "@vue/cli-plugin-babel": "^4.2.2",
+    "@vue/cli-plugin-eslint": "^4.2.2",
+    "@vue/cli-service": "^4.0.0",
+    "@vue/eslint-config-standard": "^5.0.0",
     "babel-eslint": "^10.0.1",
-    "eslint": "^5.16.0",
-    "eslint-plugin-vue": "^5.0.0",
+    "eslint": "^6.0.0",
+    "eslint-plugin-import": "^2.20.1",
+    "eslint-plugin-node": "^11.0.0",
+    "eslint-plugin-promise": "^4.2.1",
+    "eslint-plugin-standard": "^4.0.1",
+    "eslint-plugin-vue": "^6.0.0",
     "node-sass": "^4.13.0",
     "sass-loader": "^8.0.0",
     "vue-template-compiler": "^2.6.10"

frontend/src/views/Reader.vue

@@ -122,7 +122,7 @@ export default {
     },
 
     setOrientation () {
-      let image = this.$refs.currentImage
+      const image = this.$refs.currentImage
 
       if (image.width < image.height) {
         this.orientation = 'vertical'