🎨(frontend) Minor refactoring

- improve condition statements
- add "no-var" rule in eslint
- remove some unnecessary variables

Signed-off-by: Zorin95670 <moittie.vincent@gmail.com>

src/frontend/packages/eslint-config-impress/common.js

@@ -56,6 +56,7 @@ const globalRules = {
     'error',
     { varsIgnorePattern: '^_', argsIgnorePattern: '^_' },
   ],
+  'no-var': 'error',
   'react/jsx-curly-brace-presence': [
     'error',
     { props: 'never', children: 'never', propElementValues: 'always' },