Add eslint as a dev-dependency; add 'Travis-CI' YAML configuration

.gitignore

@@ -1,3 +1,6 @@
+package-lock.json
+composer.*
+vendor/
 dev/
 /config.php
 ads.php
@@ -9,5 +12,5 @@ crowdin.yaml
 *.po
 .idea/
 xgettext.*
-*/node_modules/
+/node_modules/
 /nbproject/private/

.travis.yml

@@ -0,0 +1,25 @@
+# https://docs.travis-ci.com/user/languages/javascript-with-nodejs/
+# https://medium.com/@gogl.alex/how-to-properly-set-up-eslint-with-prettier-for-vue-or-nuxt-in-vscode-e42532099a9c
+
+# os: linux (default)
+
+dist: xenial # Faster.
+
+sudo: false
+
+language: node_js
+
+node_js: 11
+
+cache: npm
+
+# install: npm ci (default)
+
+# before_script: npm run build
+
+# script: npm test (default)
+
+# Output the 'eslint' configuration.
+after_script: grep -rn eslintConfig -A 7 package.json
+
+# End.

package.json

@@ -4,7 +4,8 @@
   "description": "Remind users to update their browser in an unobtrusive way.",
   "main": "update.npm.full.js",
   "scripts": {
-    "test": "echo \"Error: no test specified\" && exit 1"
+    "fix": "# Todo: semistandard --fix",
+    "test": "eslint ./*.js # semistandard"
   },
   "repository": {
     "type": "git",
@@ -23,5 +24,19 @@
   "bugs": {
     "url": "https://github.com/browser-update/browser-update/issues"
   },
-  "homepage": "http://browser-update.org"
+  "homepage": "https://browser-update.org",
+  "eslintConfig": {
+    "env": {
+      "browser": true
+    },
+    "extends": [
+      "eslint:recommended"
+    ]
+  },
+  "devDependencies": {
+    "eslint": "^5.16.0"
+  },
+  "peerDependencies": {
+    "semistandard": "^13.0.1"
+  }
 }