JS tooling: run TS grunt tasks only when files changed

- using grunt-newer to prefix precommit tasks
- only got it to work for tslint and tsc

Not applied to:

- sasslint does not take the file arguments in a way that grunt-newer
  recognizes
- no-only-tests throws an error when used with `newer`, but it's
  sub-second runtime

scripts/grunt/default_task.js

@@ -17,8 +17,8 @@ module.exports = function (grunt) {
 
   grunt.registerTask('precommit', [
     'sasslint',
-    'exec:tslint',
-    'exec:tsc',
+    'newer:exec:tslint',
+    'newer:exec:tsc',
     'no-only-tests'
   ]);
 

scripts/grunt/options/exec.js

@@ -2,8 +2,14 @@ module.exports = function (config, grunt) {
   'use strict';
 
   return {
-    tslint: 'node ./node_modules/tslint/lib/tslintCli.js -c tslint.json --project ./tsconfig.json',
-    tsc: 'yarn tsc --noEmit',
+    tslint: {
+      command: 'node ./node_modules/tslint/lib/tslintCli.js -c tslint.json --project ./tsconfig.json',
+      src: ['public/app/**/*.ts*'],
+    },
+    tsc: {
+      command: 'yarn tsc --noEmit',
+      src: ['public/app/**/*.ts*'],
+    },
     jest: 'node ./node_modules/jest-cli/bin/jest.js --maxWorkers 2',
     webpack: 'node ./node_modules/webpack/bin/webpack.js --config scripts/webpack/webpack.prod.js',
   };