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# Lodash IndexOf
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The lodash.indexof package provides the lodash `_.indexOf` method as a standalone Node.js module, enabling efficient array searching functionality with SameValueZero equality comparisons.
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## Package Information
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- **Package Name**: lodash.indexof
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- **Package Type**: npm  
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- **Language**: JavaScript
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- **Installation**: `npm install lodash.indexof` (recommended: `npm i -g npm` first to update npm)
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- **Version**: 4.0.5
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## Core Imports
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```javascript
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const indexOf = require('lodash.indexof');
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```
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For ES modules (with compatible bundlers):
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```javascript
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import indexOf from 'lodash.indexof';
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```
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## Basic Usage
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```javascript
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const indexOf = require('lodash.indexof');
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// Basic search
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indexOf([1, 2, 1, 2], 2);
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// => 1
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// Search from specific index
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indexOf([1, 2, 1, 2], 2, 2);  
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// => 3
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// Value not found
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indexOf([1, 2, 3], 4);
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// => -1
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// Handle NaN values correctly
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indexOf([1, NaN, 3], NaN);
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// => 1
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```
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## Capabilities
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### Array Index Search
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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.
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```javascript { .api }
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/**
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 * Gets the index at which the first occurrence of `value` is found in `array`
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 * using SameValueZero for equality comparisons. If `fromIndex` is negative, 
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 * it's used as the offset from the end of `array`.
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 *
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 * @param {Array} array - The array to inspect
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 * @param {*} value - The value to search for  
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 * @param {number} [fromIndex=0] - The index to search from
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 * @returns {number} Returns the index of the matched value, else -1
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 */
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function indexOf(array, value, fromIndex);
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```
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**Parameters:**
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- `array` (Array): The array to inspect
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- `value` (*): The value to search for
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- `fromIndex` (number, optional): The index to search from (default: 0)
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**Returns:**
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- (number): The index of the matched value, else -1
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**Usage Examples:**
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```javascript
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const indexOf = require('lodash.indexof');
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// Basic usage
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indexOf([1, 2, 1, 2], 2);
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// => 1
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// Search from specific index
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indexOf([1, 2, 1, 2], 2, 2);
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// => 3
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// Negative fromIndex (offset from end)
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indexOf([1, 2, 1, 2], 1, -2);
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// => 2
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// Handle special values
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indexOf([1, NaN, 3], NaN);  // Uses SameValueZero
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// => 1
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indexOf([1, undefined, 3], undefined);
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// => 1
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indexOf([1, null, 3], null);
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// => 1
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// Empty array
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indexOf([], 1);
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// => -1
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// Value not found
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indexOf([1, 2, 3], 'a');
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// => -1
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```
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## Implementation Details
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The function uses SameValueZero equality comparison, which means:
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- It correctly identifies NaN values (unlike strict equality `===`)
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- It treats +0 and -0 as equal
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- It handles edge cases with undefined and null values consistently
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The implementation includes optimizations for:
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- Negative fromIndex values (converted to positive offset)
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- Bounds checking to prevent out-of-range errors
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- Special NaN handling through internal `baseIsNaN` function
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- Performance optimization through direct array access patterns
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## Additional Resources
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- [Official lodash documentation](https://lodash.com/docs#indexOf)
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- [Package source on GitHub](https://github.com/lodash/lodash/blob/4.0.5-npm-packages/lodash.indexof)