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tessl/npm-lodash-isnan

The lodash method `_.isNaN` exported as a module for reliable NaN detection.

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lodash.isnan

lodash.isnan provides a reliable NaN (Not a Number) detection function that implements the same behavior as Number.isNaN. Unlike the global isNaN function which incorrectly returns true for undefined and other non-number values, this implementation only returns true for actual NaN values, providing consistent and correct NaN detection.

Package Information

  • Package Name: lodash.isnan
  • Package Type: npm
  • Language: JavaScript
  • Installation: npm install lodash.isnan

Core Imports

const isNaN = require('lodash.isnan');

For ES modules:

import isNaN from 'lodash.isnan';

Basic Usage

const isNaN = require('lodash.isnan');

// Test with actual NaN values
console.log(isNaN(NaN));                    // => true
console.log(isNaN(new Number(NaN)));        // => true

// Test with non-NaN values that global isNaN incorrectly handles
console.log(isNaN(undefined));              // => false (global isNaN returns true!)
console.log(isNaN('hello'));                // => false (global isNaN returns true!)
console.log(isNaN({}));                     // => false (global isNaN returns true!)

// Test with regular numbers
console.log(isNaN(42));                     // => false
console.log(isNaN('42'));                   // => false
console.log(isNaN(Infinity));               // => false
console.log(isNaN(-Infinity));              // => false

Capabilities

NaN Detection

Checks if a value is NaN using the same logic as Number.isNaN, providing reliable NaN detection that doesn't have the issues of the global isNaN function.

/**
 * Checks if `value` is `NaN`.
 *
 * **Note:** This method is based on `Number.isNaN` and is not the same as
 * global `isNaN` which returns `true` for `undefined` and other non-number values.
 *
 * @static
 * @memberOf _
 * @since 0.1.0
 * @category Lang
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is `NaN`, else `false`.
 */
function isNaN(value): boolean

Key Features:

  • Based on Number.isNaN behavior for correct NaN detection
  • Only returns true for actual NaN values (primitive or Number object)
  • Returns false for undefined, strings, objects, and other non-number values
  • Handles both primitive numbers and Number objects correctly
  • Performs proper type checking before NaN comparison

Usage Examples:

const isNaN = require('lodash.isnan');

// Correct NaN detection
isNaN(NaN);                    // => true
isNaN(new Number(NaN));        // => true

// Correctly identifies non-NaN values
isNaN(undefined);              // => false
isNaN('string');               // => false
isNaN({});                     // => false
isNaN([]);                     // => false
isNaN(null);                   // => false

// Numbers (including special numbers) are not NaN
isNaN(42);                     // => false
isNaN(0);                      // => false
isNaN(-42);                    // => false
isNaN(Infinity);               // => false
isNaN(-Infinity);              // => false
isNaN(Number.MAX_VALUE);       // => false
isNaN(Number.MIN_VALUE);       // => false

// Comparison with global isNaN
isNaN(undefined);              // => false (lodash.isnan)
window.isNaN(undefined);       // => true  (global isNaN - incorrect!)

isNaN('123');                  // => false (lodash.isnan)
window.isNaN('123');           // => false (global isNaN - happens to be correct)

isNaN('hello');                // => false (lodash.isnan)
window.isNaN('hello');         // => true  (global isNaN - incorrect!)

Implementation Details

The function uses a two-step process for reliable NaN detection:

  1. Type Check: First verifies if the value is a number (primitive or Number object) using typeof check and Object.prototype.toString
  2. NaN Check: Then uses the unique property of NaN that it's not equal to itself (value != +value)

This approach ensures that only actual number values are tested for NaN, avoiding the false positives that occur with the global isNaN function when it attempts to coerce non-numbers to numbers before testing.

Error Handling

This function does not throw any errors. It safely handles all JavaScript value types including:

  • Primitives: number, string, boolean, undefined, null, symbol, bigint
  • Objects: Plain objects, arrays, functions, dates, regular expressions
  • Special values: NaN, Infinity, -Infinity

All input values are processed safely and return the appropriate boolean result.

docs

index.md

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