defaultTo()

defaultTo<T, D>(value, defaultValue): T | D

Returns the value if it's not null, undefined, or NaN; otherwise returns the default value.

remarque

Unlike ?? (nullish coalescing), this also handles NaN.

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Type Parameters

T: T

The type of the value.

D: D

The type of the default value.

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Parameters

value: T | null | undefined

The value to check.

defaultValue: D

The default value.

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Returns: T | D

The value if valid, otherwise the default value.

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Since

2.0.0

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Also known as

defaultTo (Lodash, es-toolkit, Remeda, Ramda) · getOrElse (Effect) · ❌ (Radashi, Modern Dash, Antfu)

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Example

defaultTo(1, 10);         // => 1
defaultTo(undefined, 10); // => 10
defaultTo(null, 10);      // => 10
defaultTo(NaN, 10);       // => 10

// Compare with ?? operator
NaN ?? 10;                // => NaN
defaultTo(NaN, 10);       // => 10

// Type narrowing
const value: string | undefined = getValue();
const result = defaultTo(value, 'default'); // => string

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How it works?

Returns the value if valid, otherwise returns the default value. Unlike ??, also handles NaN.

Comparison with ??

Value	??	defaultTo
1	1	1
null	default	default
undefined	default	default
NaN	NaN	default

NaN Handling

Use Case

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Use Cases

Handle NaN from calculations 📌

Provide fallback values when calculations might produce NaN. Unlike ??, handles NaN which is a common edge case.

#NaN#calculations#fallback#math#parsing

defaultTo(parseInt('invalid'), 0); // => 0 (NaN falls back)
parseInt('invalid') ?? 0;          // => NaN (?? doesn't handle NaN)

Safe division with fallback 📌

Handle division edge cases where both operands are zero (0/0 = NaN).

#division#safe#fallback#zero#math

defaultTo(0 / 0, 0);             // => 0 (NaN falls back)
defaultTo(sum / nums.length, 0); // => 0 for empty array (0/0 = NaN)

Resolve text direction with fallback

Resolve the document direction with a fallback when the attribute is missing. Essential for bidirectional text support in design systems.

#RTL#LTR#direction#fallback#i18n#design system

const getDirection = (element: HTMLElement) =>
  defaultTo(element.getAttribute("dir"), "ltr");

// Returns "rtl" if set, "ltr" as fallback
const dir = getDirection(document.documentElement);
applyDirectionalStyles(dir);

Fallback overlay z-index when not specified

Provide a default z-index for overlays when none is configured. Perfect for overlay systems with optional z-index configuration.

#overlay#z-index#fallback#default#design system

const overlayZIndex = defaultTo(config.zIndex, 1000);
overlay.style.zIndex = String(overlayZIndex);

Config value resolution with nullish fallback

Resolve configuration values handling null, undefined, and NaN.

#config#resolution#fallback#nullish#settings

defaultTo(config.timeout, 5000);   // => 5000 if undefined
defaultTo(config.threshold, 0.5);  // => 0.5 if NaN