Lodash IndexOf

The lodash.indexof package provides the lodash _.indexOf method as a standalone Node.js module, enabling efficient array searching functionality with SameValueZero equality comparisons.

Package Information

• Package Name: lodash.indexof
• Package Type: npm
• Language: JavaScript
• Installation: npm install lodash.indexof (recommended: npm i -g npm first to update npm)
• Version: 4.0.5

Core Imports

const indexOf = require('lodash.indexof');

For ES modules (with compatible bundlers):

import indexOf from 'lodash.indexof';

Basic Usage

const indexOf = require('lodash.indexof');

// Basic search
indexOf([1, 2, 1, 2], 2);
// => 1

// Search from specific index
indexOf([1, 2, 1, 2], 2, 2);  
// => 3

// Value not found
indexOf([1, 2, 3], 4);
// => -1

// Handle NaN values correctly
indexOf([1, NaN, 3], NaN);
// => 1

Capabilities

Array Index Search

Gets the index at which the first occurrence of a value is found in an array using SameValueZero equality comparisons. If fromIndex is negative, it's used as the offset from the end of array.

/**
 * Gets the index at which the first occurrence of `value` is found in `array`
 * using SameValueZero for equality comparisons. If `fromIndex` is negative, 
 * it's used as the offset from the end of `array`.
 *
 * @param {Array} array - The array to inspect
 * @param {*} value - The value to search for  
 * @param {number} [fromIndex=0] - The index to search from
 * @returns {number} Returns the index of the matched value, else -1
 */
function indexOf(array, value, fromIndex);

Parameters:

• array (Array): The array to inspect
• value (*): The value to search for
• fromIndex (number, optional): The index to search from (default: 0)

Returns:

• (number): The index of the matched value, else -1

Usage Examples:

const indexOf = require('lodash.indexof');

// Basic usage
indexOf([1, 2, 1, 2], 2);
// => 1

// Search from specific index
indexOf([1, 2, 1, 2], 2, 2);
// => 3

// Negative fromIndex (offset from end)
indexOf([1, 2, 1, 2], 1, -2);
// => 2

// Handle special values
indexOf([1, NaN, 3], NaN);  // Uses SameValueZero
// => 1

indexOf([1, undefined, 3], undefined);
// => 1

indexOf([1, null, 3], null);
// => 1

// Empty array
indexOf([], 1);
// => -1

// Value not found
indexOf([1, 2, 3], 'a');
// => -1

Implementation Details

The function uses SameValueZero equality comparison, which means:

• It correctly identifies NaN values (unlike strict equality ===)
• It treats +0 and -0 as equal
• It handles edge cases with undefined and null values consistently

The implementation includes optimizations for:

• Negative fromIndex values (converted to positive offset)
• Bounds checking to prevent out-of-range errors
• Special NaN handling through internal baseIsNaN function
• Performance optimization through direct array access patterns

Additional Resources

• Official lodash documentation
• Package source on GitHub