Declaring a variable with let or const that already exists in the same scope.
Variables declared with `let` or `const` cannot be re-declared within the same block scope. Attempting to redeclare them throws a compile-time `SyntaxError`.
Accidentally reusing variable names in the same block, or copy-pasting code blocks without renaming variables.
1let total = 100;2// ... 20 lines later ...3let total = 200; // SyntaxError: Identifier 'total' has already been declared1let total = 100;2total = 200; // Correct: reassigning without redeclaring3 4// OR use distinct variable names if representing different values5const initialTotal = 100;6const finalTotal = 200;Simulate standard system builds to trigger compiler trace records and track memory crashes locally.
Unlike `var` (which permits redeclaration and hoist overrides), `let` and `const` enforce block-level single declaration rules.