refactor(gulp): Dry out linting task

tasks/gulp-eslint.js

@@ -1,42 +1,21 @@
 import gulp from 'gulp';
 import eslint from 'gulp-eslint';
 
-// TODO lint client
+const SERVER_FILES = [
-// TDOO separate linting cong between
-// TODO lint gulp tasks, tests, ...?
-// TODO what about prefer-const rule?
-// TODO remove estraverse dependency once https://github.com/adametry/gulp-eslint/issues/117 sorted out
-gulp.task('lint:server', () => {
-  return gulp
-    .src([
   './website/src/**/api-v3/**/*.js',
   // Comment these out in develop, uncomment them in api-v3
   // './website/src/models/user.js',
   // './website/src/server.js'
-    ])
+];
-    .pipe(eslint())
+const COMMON_FILES = [
-    .pipe(eslint.format())
-    .pipe(eslint.failAfterError());
-});
-
-gulp.task('lint:common', () => {
-  return gulp
-    .src([
   './common/script/**/*.js',
   // @TODO remove these negations as the files are converted over.
   '!./common/script/index.js',
   '!./common/script/content/index.js',
   '!./common/script/src/**/*.js',
   '!./common/script/public/**/*.js',
-    ])
+];
-    .pipe(eslint())
+const TEST_FILES = [
-    .pipe(eslint.format())
-    .pipe(eslint.failAfterError());
-});
-
-gulp.task('lint:tests', () => {
-  return gulp
-    .src([
   './test/**/*.js',
   // @TODO remove these negations as the test files are cleaned up.
   '!./test/api-legacy/**/*',
@@ -46,8 +25,31 @@ gulp.task('lint:tests', () => {
   '!./test/e2e/**/*',
   '!./test/server_side/**/*',
   '!./test/spec/**/*',
-    ])
+];
-    .pipe(eslint({
+
+let linter = (src, options) => {
+  return gulp
+    .src(src)
+    .pipe(eslint(options))
+    .pipe(eslint.format())
+    .pipe(eslint.failAfterError());
+}
+
+// TODO lint client
+// TDOO separate linting cong between
+// TODO lint gulp tasks, tests, ...?
+// TODO what about prefer-const rule?
+// TODO remove estraverse dependency once https://github.com/adametry/gulp-eslint/issues/117 sorted out
+gulp.task('lint:server', () => {
+  return linter(SERVER_FILES);
+});
+
+gulp.task('lint:common', () => {
+  return linter(COMMON_FILES);
+});
+
+gulp.task('lint:tests', () => {
+  let options = {
     rules: {
       'max-nested-callbacks': 0,
       'no-unused-expressions': 0,
@@ -61,17 +63,17 @@ gulp.task('lint:tests', () => {
       'sinon': true,
     },
     plugins: [ 'mocha' ],
-    }))
+  };
-    .pipe(eslint.format())
+
-    .pipe(eslint.failAfterError());
+  return linter(TEST_FILES, options);
 });
 
 gulp.task('lint', ['lint:server', 'lint:common', 'lint:tests']);
 
 gulp.task('lint:watch', () => {
   gulp.watch([
-    './website/src/**/*.js',
+    SERVER_FILES,
-    './common/script/**/*.js',
+    COMMON_FILES,
-    './test/**/*.js',
+    TEST_FILES,
   ], ['lint']);
 });