nullishCoalescingOperators

Prefer nullish coalescing operator (??) over logical OR (||) for nullish values.

✅ This rule is included in the ts stylistic and stylisticStrict presets.

The logical OR operator (||) returns the right operand when the left operand is any falsy value, including 0, "", false, null, and undefined. The nullish coalescing operator (??) only returns the right operand when the left operand is null or undefined, preserving other falsy values.

When the left operand can only be nullish (not other falsy values like 0, "", or false), using ?? more clearly expresses the intent and avoids accidentally replacing legitimate falsy values.

Examples

❌ Incorrect

let value: string | null = null;
const result = value || "default";

let value: number | undefined = undefined;
const result = value || 0;

function getValue(): object | null {
  return null;
}
const result = getValue() || {};

✅ Correct

let value: string | null = null;
const result = value ?? "default";

let value: number | undefined = undefined;
const result = value ?? 0;

function getValue(): object | null {
  return null;
}
const result = getValue() ?? {};

let value: string = "";
const result = value || "default";

let value: number = 0;
const result = value || 1;

Options

This rule is not configurable.

When Not To Use It

If your codebase intentionally uses || to handle all falsy values uniformly, or if you have a large legacy codebase where migrating to ?? would require extensive changes, you may want to disable this rule.

Some projects also prefer || for its broader falsy checking behavior when the distinction between nullish and other falsy values is not important.

Further Reading

• MDN: Nullish coalescing operator (??)
• MDN: Logical OR (||)

Equivalents in Other Linters

• ESLint: @typescript-eslint/prefer-nullish-coalescing