No Constant Condition

javascript.no_constant_condition

Severity

low

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Reliability

Language

JavaScript

Description

Reports if, while, do…while, for, and ternary expressions whose condition is a constant value known at parse time — a literal number, string, boolean, null, regex, or any object / array / template literal. The condition always evaluates to the same truthiness, so the branch is either dead code or an unconditional loop entry.

The idiomatic infinite-loop forms while (true) {…} and do {…} while (true) are explicitly permitted to keep the rule usable in real code bases. for (;;) {…} is also accepted because the condition slot is empty (no constant expression).

Rationale

if (false) {…} is dead code and almost always a leftover from debugging or a typo (the author meant if (flag === false) or similar).
if ([]) {…} is more subtle: empty arrays and objects are truthy in JavaScript. The branch always runs, even though many developers expect the opposite. Using a literal as the condition is a known mistake.
In a for header, a literal condition produces an infinite loop unless something inside breaks — the explicit while (true) form is clearer and is the form the rule allows.

// Bad
if (false) {
  legacyCleanup();    // never runs
}

if ([]) {            // always runs — empty arrays are truthy
  reset();
}

const flag = (true) ? "on" : "off";   // ternary always picks the first branch

Remediation

Replace the constant with the actual variable, expression, or feature flag the author intended. For intentional infinite loops, prefer while (true) {…} (which the rule allows) or for (;;) {…}.

// Good
if (config.legacyMode) {
  legacyCleanup();
}

if (items.length === 0) {
  reset();
}

const flag = settings.enabled ? "on" : "off";

References

MDN — Truthy