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tessl/npm-dlv

Safely get a dot-notated property within an object with optional default values.

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dlv

dlv is a minimal utility library (only 130 bytes) that provides safe access to deeply nested object properties using dot notation or array paths. It prevents runtime errors when accessing non-existent nested properties and supports default values when the full key path is missing or undefined.

Package Information

  • Package Name: dlv
  • Package Type: npm
  • Language: JavaScript
  • Installation: npm install dlv

Core Imports

ES Modules:

import dlv from 'dlv';

CommonJS:

const dlv = require('dlv');

UMD/Browser:

<script src="path/to/dlv.umd.js"></script>
<!-- Available as global 'dlv' -->

Basic Usage

import dlv from 'dlv';

const obj = {
  a: {
    b: {
      c: 1,
      d: undefined,
      e: null
    }
  }
};

// Use string dot notation for keys
const value1 = dlv(obj, 'a.b.c'); // Returns: 1

// Or use an array of keys
const value2 = dlv(obj, ['a', 'b', 'c']); // Returns: 1

// Returns undefined if the full key path does not exist
const value3 = dlv(obj, 'a.b.f'); // Returns: undefined

// Optional default value when path is missing or undefined
const value4 = dlv(obj, 'a.b.f', 'default'); // Returns: 'default'
const value5 = dlv(obj, 'a.b.d', 'default'); // Returns: 'default' (d is undefined)

// Falsy values are preserved if they exist at the target path
const value6 = dlv(obj, 'a.b.e', 'default'); // Returns: null (not 'default')

// Handles undefined objects gracefully
const value7 = dlv(undefined, 'a.b.c'); // Returns: undefined
const value8 = dlv(undefined, 'a.b.c', 'default'); // Returns: 'default'

Capabilities

Safe Property Access

Safely retrieves a dot-notated property from within an object without throwing errors for non-existent paths.

/**
 * Safely get a dot-notated property within an object
 * @param {any} obj - The object to traverse
 * @param {string|Array} key - Dot-notated path string (e.g., 'a.b.c') or array of keys (e.g., ['a', 'b', 'c'])
 * @param {any} [def] - Default value to return if the full key path doesn't exist or resolves to undefined
 * @returns {any} The value at the specified path, or the default value, or undefined
 */
function dlv(obj, key, def);

Parameter Details:

  • obj (any): The object to traverse. Can be any value including null, undefined, or non-objects
  • key (string|Array):
    • String: Dot-notated path like 'a.b.c' or 'user.profile.name'
    • Array: Array of keys like ['a', 'b', 'c'] or ['user', 'profile', 'name']
  • def (any, optional): Default value returned when:
    • The full key path doesn't exist in the object
    • The value at the path is undefined
    • The input object is null or undefined

Return Value:

  • The actual value at the specified path if it exists and is not undefined
  • The default value (def) if the path doesn't exist, resolves to undefined, or the object is null/undefined
  • undefined if no default is provided and the path doesn't exist or resolves to undefined

Key Behaviors:

  • Path Resolution: Supports both string dot-notation ('a.b.c') and array notation (['a', 'b', 'c'])
  • Safe Traversal: Never throws errors for missing intermediate properties
  • Undefined Handling: Returns default value when target property is undefined, but preserves other falsy values (0, false, null, '')
  • Object Safety: Handles null/undefined input objects gracefully without errors
  • Default Preservation: Only uses default value for undefined results, not for other falsy values like null, 0, or false

Usage Examples:

import dlv from 'dlv';

// Complex nested object
const user = {
  profile: {
    personal: {
      name: 'Alice',
      age: 0,
      active: false
    },
    settings: {
      theme: null,
      notifications: undefined
    }
  }
};

// Basic access
dlv(user, 'profile.personal.name'); // 'Alice'
dlv(user, ['profile', 'personal', 'name']); // 'Alice'

// Missing path
dlv(user, 'profile.work.title'); // undefined
dlv(user, 'profile.work.title', 'Unknown'); // 'Unknown'

// Falsy value preservation
dlv(user, 'profile.personal.age'); // 0 (not undefined)
dlv(user, 'profile.personal.active'); // false (not undefined)
dlv(user, 'profile.settings.theme'); // null (not undefined)

// Undefined handling
dlv(user, 'profile.settings.notifications'); // undefined
dlv(user, 'profile.settings.notifications', 'disabled'); // 'disabled'

// Edge cases
dlv(null, 'any.path'); // undefined
dlv(null, 'any.path', 'default'); // 'default'
dlv(user, '', 'default'); // 'default' (empty path)

// API responses
const apiResponse = {
  data: {
    users: [
      { id: 1, meta: { created: '2023-01-01' } },
      { id: 2 } // missing meta
    ]
  }
};

const firstUserCreated = dlv(apiResponse, 'data.users.0.meta.created', 'N/A');
const secondUserCreated = dlv(apiResponse, 'data.users.1.meta.created', 'N/A');
// firstUserCreated: '2023-01-01'
// secondUserCreated: 'N/A'

Error Handling:

  • Throws an error when the key parameter is undefined (no path provided)
  • Does not throw errors for any other input combinations
  • Gracefully handles all types of input objects including primitives, null, and undefined

Types

Since dlv is written in vanilla JavaScript, it doesn't include built-in TypeScript types, but the function signature would be:

/**
 * TypeScript type definitions for dlv (not included in package)
 */
declare function dlv<T = any>(
  obj: any,
  key: string | (string | number)[],
  def?: T
): T | undefined;

export default dlv;

Install with Tessl CLI

npx tessl i tessl/npm-dlv
Workspace
tessl
Visibility
Public
Created
Last updated
Describes
npmpkg:npm/dlv@1.1.x
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