require-no-implicit-returns

Require "noImplicitReturns": true in compilerOptions so that TypeScript reports an error when a function does not explicitly return a value on all code paths.

Targeted pattern scope

The compilerOptions.noImplicitReturns field in any tsconfig*.json file.

What this rule reports

This rule reports when compilerOptions.noImplicitReturns is absent or explicitly set to false.

Why this rule exists

When a function is declared with a non-void return type but some of its code paths reach the end without returning a value, JavaScript silently returns undefined from that branch:

function getLabel(code: number): string {
    if (code === 1) {
        return "success";
    }
    // ← no return here — TypeScript would allow this without noImplicitReturns
    // at runtime, callers receive `undefined` instead of a string
}

With noImplicitReturns: true, TypeScript reports an error on this function, requiring every code path to explicitly return a value (or be typed as returning string | undefined).

Common scenarios where this catches real bugs:

• Functions with complex if/else or switch chains where a new branch is added but the return statement is forgotten.
• Methods in classes where the default return is accidentally undefined due to an incomplete migration.
• Arrow functions used as callbacks that are expected to always produce a value.

The auto-fixer adds "noImplicitReturns": true to compilerOptions.

❌ Incorrect

{
    "compilerOptions": {
        "target": "ES2022",
        "module": "NodeNext"
    }
}

noImplicitReturns is absent; functions that silently return undefined on some paths are not reported.

{
    "compilerOptions": {
        "noImplicitReturns": false
    }
}

Explicitly disabled.

✅ Correct

{
    "compilerOptions": {
        "noImplicitReturns": true
    }
}

All code paths in non-void functions must explicitly return a value.

When not to use it

Disable this rule in projects that deliberately use implicit undefined returns as a shorthand for early-exit patterns, or when migrating a large JavaScript codebase where fixing every implicit return at once is not feasible. In those cases, track the suppressions and enable the rule incrementally.

Package documentation

Rule catalog ID: R033

Further reading

• TypeScript handbook — noImplicitReturns