IDEA9103 Chap.6 Variables, Constants and Primitive Types

Use let when the algorithm deliberately reassigns the binding, such as an animation counter or changing position. Use const for stable references and values whose binding should not be replaced.

Undefined commonly appears when a binding or argument has no assigned value. Null is an intentional empty value supplied by the programmer, and the captured functions use it to request a generated fallback.

Yes. Const protects the stored reference from reassignment. Methods can still change attributes on the element that reference points to, which is common in DOM based creative coding.

Trace every statement that refers to the binding and circle each assignment. A const declaration matches when the reference is established once and later statements only read it or mutate the referenced object. A let declaration matches when a later event deliberately replaces the stored value. If the trace contains an accidental reassignment, repair that statement rather than weakening the declaration.

The keyword should communicate the state story a reader will actually observe during execution.

Separate names preserve separate design decisions. A single vague size value may work for a square, but it hides whether later geometry depends on horizontal extent, vertical extent or both. With canvasWidth and canvasHeight, a trace can change one dimension while holding the other constant and reveal which expressions respond.

The names also make attribute assignment easier to audit because each value carries its intended role into the DOM code instead of relying on its position in a sequence.

Record the binding name, the value after each assignment, its type and the statement that caused the change. Include the observation point because a console log before a reassignment reports a different state from one after it. This small ledger distinguishes declaration, first assignment and later reassignment.

It also exposes unintended coupling: if changing particleCount alters a supposedly fixed canvasWidth, the trace identifies the expression where the two responsibilities became entangled.

Convert at the boundary where external text enters a calculation and only after naming the type the next operation requires. For example, a text field may supply digit characters that must become a number before arithmetic. Log both the incoming value and typeof result, perform the conversion once, then continue with a clear numeric contract.

Scattered conversions can hide a modelling problem and make later concatenation or addition depend on accidental coercion rather than an explicit creative-coding decision.

Treat them as separate questions. The declaration keyword describes whether the binding may be reassigned, while the current value determines which operations make sense at that moment. A let binding can hold a number at one step and, although usually undesirable, a string later; const prevents reassignment but does not make the referenced object immutable. Record both the keyword contract and each observed type.

When behaviour is surprising, identify whether the failure came from an unauthorised state change, an unsuitable value type or an operation that assumed a different contract.