Required override keyword

tsconfig.json

@@ -40,6 +40,7 @@
     // "noImplicitReturns": true,                   /* Report error when not all code paths in function return a value. */
     // "noFallthroughCasesInSwitch": true,          /* Report errors for fallthrough cases in switch statement. */
     // "noUncheckedIndexedAccess": true,            /* Include 'undefined' in index signature results */
+    "noImplicitOverride": true,                     /* Ensure overriding members in derived classes are marked with an 'override' modifier. */
     // "noPropertyAccessFromIndexSignature": true,  /* Require undeclared properties from index signatures to use element accesses. */
 
     /* Module Resolution Options */