Added ESLint pipeline into Gulp

backend/gulpfile.babel.js

@@ -3,9 +3,21 @@ import browserify from 'browserify';
 import gulp from 'gulp';
 import prettier from 'gulp-prettier';
 import header from 'gulp-header';
+import eslint from 'gulp-eslint-new';
+
+import pkg from './package.json';
 
 const DEST_FILE = 'sub-store.min.js';
 
+export function lint() {
+	return gulp
+		.src('src/**/*.js')
+		.pipe(eslint({ fix: true }))
+		.pipe(eslint.fix())
+		.pipe(eslint.format())
+		.pipe(eslint.failAfterError());
+}
+
 export function styles() {
 	return gulp
 		.src('src/**/*.js')
@@ -23,11 +35,7 @@ export function styles() {
 export function scripts() {
 	return browserify('src/main.js')
 		.transform('babelify', {
-			presets: [
-        [
-          '@babel/preset-env'
-        ]
-			]
+			presets: [ [ '@babel/preset-env' ] ]
 		})
 		.plugin('tinyify')
 		.bundle()
@@ -35,14 +43,12 @@ export function scripts() {
 }
 
 export function banner() {
-	const pkg = require('./package.json');
-
 	return gulp
 		.src(DEST_FILE)
 		.pipe(header(fs.readFileSync('./banner', 'utf-8'), { pkg, updated: new Date().toLocaleString() }))
 		.pipe(gulp.dest((file) => file.base));
 }
 
-const build = gulp.series(styles, scripts, banner);
+const build = gulp.series(lint, styles, scripts, banner);
 
 export default build;