frontend: check for strict equal eslint rule

It is considered good practice to use the type-safe equality
operators === and !== instead of their regular counterparts
 == and !=.

https://eslint.org/docs/latest/rules/eqeqeq

Author: thisconnect

frontends/web/.eslintrc.json

@@ -20,6 +20,7 @@
     "jsx-a11y/alt-text" : 0,
     "jsx-quotes": ["error", "prefer-double"],
     "keyword-spacing": "error",
+    "eqeqeq": "error",
     "no-multi-spaces": "error",
     "no-trailing-spaces": "error",
     "object-curly-spacing": ["error", "always"],