Lodash _.defaults() Method

Beginner
5 min read
Updated: Nov 2026
5 examples
Object
Decorative image with the word DEFAULTS

Definition

Assigns source properties to the destination for keys that are still undefined. Sources apply left to right; once a property is set, later values for that key are ignored. Since Lodash 0.1.0.

Pass the object and path or keys shown below. Check whether the helper mutates or returns a new object.

Syntax

Call _.defaults. Start with this line.

Lodash
_.defaults(object, ...sources)
CallWhat it does
_.defaults(object, ...sources)Primary signature.
_.defaults(object)Work with an object’s keys, values, or paths.

Prefer import defaults from "lodash/defaults" when you want a smaller bundle.

Library declarations
Lodash
_.defaults(object, ...sources)

Parameters

ParameterDescription
objectRequired. Destination (mutated and returned)
...sourcesOptional. Default providers (left → right)

Return Value

Return ValueDescription
*The value returned by _.defaults().

Lodash Examples

Example 1 — Official: Keep Defined, Fill Missing

Existing keys win; new keys come from sources.

Lodash
_.defaults({ a: 1 }, { b: 2 }, { a: 3 });
// → { a: 1, b: 2 }
Try It Yourself

How It Works

  1. Destination already has a: 1.
  2. { b: 2 } fills the missing b.
  3. { a: 3 } cannot overwrite a.
  4. Result. { a: 1, b: 2 }.

Example 2 — vs _.assign

Defaults fill gaps; assign overwrites.

Lodash
_.defaults({ a: 1 }, { a: 3, b: 2 });
// → { a: 1, b: 2 }

_.assign({ a: 1 }, { a: 3, b: 2 });
// → { a: 3, b: 2 }
Try It Yourself

How It Works

  1. defaults. Keeps destination a: 1; adds b.
  2. assign. Later source wins → a becomes 3.
  3. Both add missing b: 2.
  4. Pick defaults for option bags; assign for merges that overwrite.

Example 3 — null vs undefined

Only undefined is treated as a gap.

Lodash
_.defaults({ a: undefined, b: null }, { a: 1, b: 2, c: 3 });
// → { a: 1, b: null, c: 3 }
Try It Yourself

How It Works

  1. a is undefined → filled with 1.
  2. b is null → kept (not a gap).
  3. c is missing → filled with 3.
  4. Tip. Normalize null first if you want it replaced too.

Example 4 — Safe Options Pattern

Merge user options onto a fresh object with factory defaults.

Lodash
var factory = { retries: 3, timeout: 1000, debug: false };
var user = { timeout: 5000 };

var opts = _.defaults({}, user, factory);
// → { timeout: 5000, retries: 3, debug: false }

user;
// → { timeout: 5000 }  // unchanged
Try It Yourself

How It Works

  1. {} is the destination — nothing is mutated that you care about.
  2. user applies first → timeout: 5000.
  3. factory fills the remaining undefined keys.
  4. Pattern. Classic “options with defaults” helper.

Example 5 — First Source Wins

Among sources, the leftmost defining value sticks.

Lodash
_.defaults({}, { a: 1 }, { a: 2, b: 3 }, { b: 4, c: 5 });
// → { a: 1, b: 3, c: 5 }
Try It Yourself

How It Works

  1. First source sets a: 1.
  2. Second cannot change a; sets b: 3.
  3. Third cannot change b; sets c: 5.
  4. Order matters — put higher-priority defaults earlier.
Compatibility

Browser & Runtime Support

_.defaults is a Lodash Object helper (since 0.1.0). It runs anywhere Lodash 4.x runs — modern browsers (CDN or bundle) and Node.js / Bun / Deno with npm install lodash.

✓ Stable · Lodash 0.1.0+

_.defaults()

Available in [email protected] full builds and the lodash/defaults modular import. Works in evergreen browsers and current Node LTS when Lodash is installed.

100% With Lodash 4.x
Google Chrome Supported · Desktop & Mobile
Full support
Mozilla Firefox Supported · Desktop & Mobile
Full support
Apple Safari Supported · macOS & iOS
Full support
Microsoft Edge Supported · Chromium
Full support
Internet Explorer No native support · Use a polyfill
Polyfill
Opera Supported · Modern versions
Full support
Samsung Internet Supported · Android
Full support
Bun Supported · JavaScript runtime
Supported
Deno Supported · JavaScript runtime
Supported
Node.js Supported · Server runtime
Supported
Android WebView Supported · Modern WebView
Full support
_.defaults Lodash 0.1.0+

Bottom line: Safe for production once Lodash is loaded. Prefer import defaults from "lodash/defaults". Use defaultsDeep when nested objects need gap-filling too.

Frequently Asked Questions

_.defaults(object, ...sources) assigns source properties to the destination only where the destination value is undefined. Sources apply left to right; once a key is set, later sources are ignored for that key.
_.assign overwrites — later sources win. _.defaults only fills undefined gaps — the destination (and the first defining source) win.
No. Only undefined counts as missing. null is treated as already set.
Yes. Pass {} when you want a fresh object: _.defaults({}, userOpts, factoryDefaults).
No. Nested objects already present on the destination are left alone. Use _.defaultsDeep for recursive gap-filling.
Use import defaults from "lodash/defaults" or require("lodash/defaults"). Full build: import _ from "lodash" then _.defaults.

Next: _.defaultsDeep()

Recursively fill undefined nested properties.

_.defaultsDeep() tutorial →

About the author

Mari Selvan M P
Mari Selvan M P 🔗

Developer, cloud engineer, and technical writer

  • Experience 12 years building web and cloud systems
  • Focus Full Stack Development, AWS, and Developer Education

I write practical tutorials so students and working developers can learn by doing—from databases and APIs to deployment on AWS.

AWS Certified Developer – Associate (Credly)

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