oxc-project/oxc · error

Redundant Boolean call

Error message

Redundant Boolean call

What it means

Diagnostic from oxlint's port of the ESLint no-extra-boolean-cast rule. It fires when a Boolean(...) call sits in a position JavaScript already coerces to a boolean: an if/while/do-while/for condition, a ternary test, the operand of !, or another Boolean() argument. The surrounding context guarantees a boolean, so the cast is dead code. With enforceForInnerExpressions: true (default false) it also flags casts inside sub-expressions whose result feeds a boolean context.

Source

Thrown at crates/oxc_linter/src/rules/eslint/no_extra_boolean_cast.rs:33

    operator::{LogicalOperator, UnaryOperator},
    precedence::{GetPrecedence, Precedence},
};

use crate::{
    AstNode,
    context::LintContext,
    rule::{DefaultRuleConfig, Rule},
    utils::{get_precedence, pad_fix_with_token_boundary},
};

fn no_extra_double_negation_cast_diagnostic(span: Span) -> OxcDiagnostic {
    OxcDiagnostic::warn("Redundant double negation")
        .with_help("Remove the double negation as it will already be coerced to a boolean")
        .with_label(span)
}

fn no_extra_boolean_cast_diagnostic(span: Span) -> OxcDiagnostic {
    OxcDiagnostic::warn("Redundant Boolean call")
        .with_help("Remove the Boolean call as it will already be coerced to a boolean")
        .with_label(span)
}

#[derive(Debug, Default, Clone, JsonSchema, Deserialize)]
#[serde(rename_all = "camelCase", default, deny_unknown_fields)]
pub struct NoExtraBooleanCast {
    /// when set to `true`, in addition to checking default contexts, checks
    /// whether extra boolean casts are present in expressions whose result is
    /// used in a boolean context. See examples below. Default is `false`,
    /// meaning that this rule by default does not warn about extra booleans
    /// cast inside inner expressions.
    #[serde(alias = "enforceForLogicalOperands")]
    pub enforce_for_inner_expressions: bool,
}

declare_oxc_lint!(
    /// ### What it does

View on GitHub (pinned to e1e7af627c)

Solutions

1. Remove the cast and use the value directly (if (x) instead of if (Boolean(x))).
2. If the pattern is !!Boolean(v), drop both the call and the negations.
3. If the cast is intentional for readability, suppress the line with // oxlint-disable-next-line eslint/no-extra-boolean-cast.
4. Keep enforceForInnerExpressions: false in the rule config to avoid reports on inner expressions.

Example fix

// before
if (Boolean(user.isActive)) {
  render();
}

// after
if (user.isActive) {
  render();
}

const redundant = /\b(?:if|while)\s*\(\s*(?:!!\s*)?Boolean\s*\(/.test(source);
if (redundant) failFast('no-extra-boolean-cast will fire');

When it happens

Trigger: if (Boolean(x)) {...}; while (!!Boolean(done)) {...}; const r = Boolean(a) ? 1 : 0 (cast in the ternary test); !Boolean(visible); Boolean(Boolean(v)) (nested calls); with enforceForInnerExpressions: true: if (a && Boolean(b)) {...}.

Common situations: Defensive 'make it boolean' casts copied from older code or earlier autofixes; reviewers adding Boolean() in conditions for readability; enabling enforceForInnerExpressions during an oxlint upgrade, which suddenly flags inner expressions that default mode ignored.

Related errors

• This label '{label_name}' is unnecessary
• Unexpected implicit coercion to boolean
• Empty array binding pattern
• Empty object binding pattern
• Unexpected constant {lhs_name} on the left-hand side of a {e

AI-assisted analysis of oxc-project/oxc@e1e7af627c (2026-08-20). Data as JSON: /api/errors/56cfdf398bcae727. Report an issue: GitHub.