oxc-project/oxc · warning

Unexpected implicit coercion to number

Error message

Unexpected implicit coercion to number

What it means

The number-kind diagnostic of oxlint's no-implicit-coercion rule. It flags unary plus +value and multiplication by one (value * 1, 1 * value), the shorthand coercions to number, and recommends the explicit Number(value) call. Options control whether number coercion is checked and which shorthand forms are allowed.

Solutions

1. Use Number(value) for straight conversion.
2. Use Number.parseInt(value, 10) or Number.parseFloat when parsing strings (usually the real intent).
3. Allow the + shorthand via the rule's allow option if it is team style.
4. Turn off number checks in the rule options.

Example fix

// before
const count = +inputEl.value;

// after
const count = Number.parseInt(inputEl.value, 10);

const plusCast = /[=(,[]\s*\+\s*[A-Za-z_(]/.test(source);

const asNum = (v: unknown): number => (typeof v === 'number' ? v : Number(v));

When it happens

Trigger: const n = +input.value;; total = raw * 1;; 1 * qty used to force numeric strings into numbers; +el.dataset.count passed around as a number.

Common situations: Parsing DOM inputs, dataset attributes, and query-string params where unary plus is the habitual trick; old code-golf snippets copied from forums; a strictness sweep turning the rule on mid-project.

Related errors

• Unexpected implicit coercion to boolean
• Unexpected implicit coercion to string
• All 'var' declarations must be at the top of the function…
• Async function has no `await` expression.
• Avoid unnecessary use of .

AI-assisted analysis of oxc-project/oxc@e1e7af627c (2026-08-20). Data as JSON: /api/errors/1ef53338b06ce4ad. Report an issue: GitHub.

Appendix: source

Thrown at crates/oxc_linter/src/rules/eslint/no_implicit_coercion.rs:23

use oxc_str::CompactStr;
use oxc_syntax::operator::{AssignmentOperator, BinaryOperator, UnaryOperator};
use schemars::JsonSchema;
use serde::Deserialize;

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

fn boolean_coercion_diagnostic(span: Span) -> OxcDiagnostic {
    OxcDiagnostic::warn("Unexpected implicit coercion to boolean")
        .with_help("Use `Boolean(value)` instead")
        .with_label(span)
}

fn number_coercion_diagnostic(span: Span) -> OxcDiagnostic {
    OxcDiagnostic::warn("Unexpected implicit coercion to number")
        .with_help("Use `Number(value)` instead")
        .with_label(span)
}

fn string_coercion_diagnostic(span: Span) -> OxcDiagnostic {
    OxcDiagnostic::warn("Unexpected implicit coercion to string")
        .with_help("Use `String(value)` instead")
        .with_label(span)
}

/// Type of implicit coercion being detected
#[derive(Clone, Copy)]
enum CoercionKind {
    Boolean,
    Number,
    String,
}

View on GitHub (pinned to e1e7af627c)