Values and decisions

The idea

JavaScript values have types even though a variable does not require a type annotation. Start by separating strings, numbers, booleans, null, and undefined. A search field supplies text; arithmetic may require deliberate conversion. Use const when the binding should not change and let when reassignment is part of the algorithm. Strict equality compares without converting different types.

A default is a policy decision. The nullish operator replaces only null and undefined, while logical OR also replaces zero, false, and empty text. Write the missing-value rule before choosing an operator. In a branch, evaluate the condition first and follow only its selected path. Test a normal value, a boundary value, and an absent value to expose accidental coercion.

const requested = 0;
const limit = requested ?? 10;
console.log(limit);
console.log("4" === 4);

0
false

Zero remains a valid limit because it is not nullish. The string and number contain similar characters but are different types.