oxc-project/oxc · error · OxcDiagnostic

Expected a `for...of` loop instead of a `for` loop with this

Error message

Expected a `for...of` loop instead of a `for` loop with this simple iteration.

What it means

Raised by typescript/prefer_for_of when a `for` loop is a simple index iteration over an array (counter starts at 0, condition is index < arr.length, increment by one, and the body only uses `arr[i]` without reassigning the index or mutating the array's length). At the throw site the loop can be expressed more safely and readably as `for (const item of arr)`, eliminating off-by-one hazards. prefer_for_of_diagnostic fires from run() after the structural checks confirm the pattern is a plain iteration.

Source

Thrown at crates/oxc_linter/src/rules/typescript/prefer_for_of.rs:16

use oxc_ast::{
    AstKind,
    ast::{
        AssignmentTarget, BindingPattern, Expression, ForStatementInit, SimpleAssignmentTarget,
        VariableDeclarationKind, match_member_expression,
    },
};
use oxc_diagnostics::OxcDiagnostic;
use oxc_macros::declare_oxc_lint;
use oxc_span::{GetSpan, Span};
use oxc_syntax::operator::{AssignmentOperator, BinaryOperator, UnaryOperator, UpdateOperator};

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

fn prefer_for_of_diagnostic(span: Span) -> OxcDiagnostic {
    OxcDiagnostic::warn(
        "Expected a `for...of` loop instead of a `for` loop with this simple iteration.",
    )
    .with_help("Consider using a `for...of` loop for this simple iteration.")
    .with_label(span)
}

#[derive(Debug, Default, Clone)]
pub struct PreferForOf;

declare_oxc_lint!(
    /// ### What it does
    ///
    /// Enforces the use of a `for...of` loop instead of a `for` loop with simple iteration.
    ///
    /// ### Why is this bad?
    ///
    /// Using a `for` loop with a simple iteration over an array can be replaced with a more concise
    /// and readable `for...of` loop. `for...of` loops are easier to read and less error-prone, as they

View on GitHub (pinned to e1e7af627c)

Solutions

1. Rewrite the loop as for (const item of array) { ... }.
2. If array methods fit, use forEach/map instead.

When it happens

Trigger: Thrown at crates/oxc_linter/src/rules/typescript/prefer_for_of.rs:16 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of oxc-project/oxc@e1e7af627c (2026-08-20). Data as JSON: /api/errors/a1d2c095b2c276a2. Report an issue: GitHub.