Lodash get Third Argument Default Values

The third argument in the Lodash _.get function specifies a fallback value returned whenever the target path resolves to undefined or does not exist. Developers can provide virtually any valid JavaScript data type as this default value—including strings, numbers, booleans, objects, arrays, functions, and even null. This mechanism prevents runtime errors such as TypeError: Cannot read property of undefined when traversing deeply nested object structures.

Accepted Default Value Types

Lodash does not restrict the type of data you can pass as the third argument. Any valid JavaScript expression or value is permitted:

• Primitives: Strings, numbers, booleans, symbols, and null (e.g., 'N/A', 0, false, null).
• Complex Data Structures: Plain objects ({}), arrays ([]), sets, or maps to maintain a consistent schema for downstream processing.
• Functions: Callbacks, no-op functions (() => {}), or factory functions.
• Custom Instances: Class instances or custom prototypes.

Syntax and Basic Usage

const _ = require('lodash');

const user = {
  profile: {
    name: 'Alex'
  }
};

// String default value
const role = _.get(user, 'profile.role', 'Guest');
// Output: 'Guest'

// Array default value
const permissions = _.get(user, 'profile.permissions', []);
// Output: []

// Object default value
const settings = _.get(user, 'settings.notifications', { email: true });
// Output: { email: true }

When the Default Value Triggers

The default value is returned exclusively when the target property evaluates to undefined. This happens under two conditions:

1. The path does not exist on the target object.
2. The property explicitly holds the value undefined.

Handling Falsy Values vs. Undefined

A common misconception is that the default value triggers for all falsy values. Lodash strictly evaluates against undefined. If a resolved property contains null, false, 0, NaN, or an empty string "", Lodash returns that specific value rather than the default argument.

const config = {
  retries: 0,
  apiKey: null,
  active: false
};

_.get(config, 'retries', 3);      // Returns: 0 (not 3)
_.get(config, 'apiKey', 'secret'); // Returns: null (not 'secret')
_.get(config, 'active', true);     // Returns: false (not true)
_.get(config, 'timeout', 5000);    // Returns: 5000 (path does not exist)