sizeComparisonOperators

Enforce consistent style for .length and .size checks.

✅ This rule is included in the ts stylisticStrict presets.

This rule enforces a consistent style for checking .length and .size properties in boolean contexts.

By default, the rule prefers implicit boolean coercion (e.g., if (array.length)) for its conciseness. Alternatively, you can configure it to prefer explicit comparisons (e.g., if (array.length > 0)) for clarity.

Examples

Default (style: "coercion")

❌ Incorrect

declare const items: string[];
if (items.length > 0) {
}

declare const items: string[];
if (items.length === 0) {
}

declare const items: string[];
if (items.length !== 0) {
}

declare const mySet: Set<string>;
if (mySet.size > 0) {
}

✅ Correct

declare const items: string[];
if (items.length) {
}

declare const items: string[];
if (!items.length) {
}

declare const items: string[];
items.length && doSomething();

declare const items: string[];
const hasItems = items.length ? "yes" : "no";

declare const mySet: Set<string>;
if (mySet.size) {
}

With style: "explicit"

❌ Incorrect

declare const items: string[];
if (items.length) {
}

declare const items: string[];
if (!items.length) {
}

declare const items: string[];
items.length && doSomething();

declare const items: string[];
const hasItems = items.length ? "yes" : "no";

declare const items: string[];
Boolean(items.length);

declare const mySet: Set<string>;
if (mySet.size) {
}

✅ Correct

declare const items: string[];
if (items.length > 0) {
}

declare const items: string[];
if (items.length === 0) {
}

declare const items: string[];
if (items.length !== 0) {
}

declare const items: string[];
const count = items.length;

declare const items: string[];
const count = items.length ?? 0;

declare const items: string[];
const value = items.length || 1;

declare const mySet: Set<string>;
if (mySet.size > 0) {
}

Options

style

• Type: "coercion" | "explicit"
• Default: "coercion"

Which style to enforce:

• "coercion": Prefer implicit boolean checks like if (array.length)
• "explicit": Prefer explicit comparisons like if (array.length > 0)

When Not To Use It

If your team doesn’t have a preference for one style over the other, or if you want to allow both styles, you might prefer to disable this rule.

Further Reading

• MDN: Truthy
• MDN: Falsy

Equivalents in Other Linters

• Biome: useExplicitLengthCheck
• ESLint: unicorn/explicit-length-check
• Oxlint: unicorn/explicit-length-check