Avoid Void Operator

ID

javascript.avoid_void_operator

Severity

low

Remediation Complexity

medium

Remediation Risk

low

Remediation Effort

medium

Resource

Code Smell

Language

JavaScript

Tags

code-smell, simplification

Description

Reports the unary void operator where its result is read. void evaluates its operand and then throws the value away, always yielding undefined, so any expression built on it is a constant that does not look like one.

const result = void compute();       // FLAW — result is undefined, whatever compute returned
if (void ready) { }                  // FLAW — the condition can never be true

function pick(flag, value) {
  return flag ? void reset() : value;  // FLAW
}

Two idioms are exempt, because they are what the operator is used for today:

const nothing = void 0;              // OK — the legacy spelling of undefined
void fetchLatest();                  // OK — a deliberate discard, as a statement
button.onclick = () => void save();  // OK — a discard in an arrow body

Rationale

  • void 0 predates undefined being safe to name — before ES5 it was a writable global — and still appears in code that has to run everywhere. It is a constant, not a discarded computation, so it carries none of the confusion this rule is about.

  • A void whose own value goes nowhere, either as a statement or as the whole body of an arrow function, is the accepted way to say "this returns a promise on purpose and I am not awaiting it".

  • What is left is the shape worth reporting. To see that const result = void compute() always assigns undefined, the reader has to know that void discards — and the operator is rare enough that most readers do not.

Remediation

Decide which of the two the line meant. If the value is to be discarded, write the operand as a statement. If it is to be used, drop the operator.

compute();
const result = compute();

References

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