How to install and use is-number in a Node.js project?

Install via npm with `npm install --save is-number`, then require it in your code: `const isNumber = require('is-number');`. Use it as a function, e.g., `isNumber('123')` returns true. The README provides extensive examples for validation.

Does is-number work with TypeScript?

The library itself is JavaScript, so TypeScript users may need to install separate type definitions (e.g., from @types/is-number) or declare types manually. The README doesn't cover this, so it's an extra step for typed projects.

What's the performance difference between is-number and Number.isFinite?

is-number is optimized for edge cases and string numbers, making it slower for pure number checks but faster for non-string/number values. Benchmarks in the README show it's competitive, but for simple checks, Number.isFinite might suffice with less overhead.

Why use is-number instead of just using typeof and isFinite?

is-number handles numeric strings and edge cases like empty arrays that typeof and isFinite miss, as shown in the README where +[] returns 0 but isNumber([]) returns false. It provides a more reliable, all-in-one solution for real-world data.

How does is-number compare to lodash's _.isNumber?

is-number focuses solely on finite number detection with better edge-case handling for strings, while lodash's version is part of a larger utility library and may have different behavior for non-primitive types. is-number is lighter if you only need number validation.

Can is-number check for integers or only floats?

It checks for any finite number, including integers and floats, but doesn't distinguish between them. For integer-specific validation, you'd need to combine it with another check, e.g., `isNumber(value) && Number.isInteger(value)`.

Open-Awesome

is-number

MITJavaScript

A JavaScript utility that reliably checks if a value is a finite number, handling edge cases like strings, NaN, and Infinity.

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What is is-number?

is-number is a JavaScript utility library that reliably checks whether a value is a finite number or a numeric string. It solves the problem of inconsistent number detection in JavaScript, where naive methods like `+value` or `Number()` can produce unexpected results for edge cases like empty strings, arrays, or NaN.

Target Audience

JavaScript and Node.js developers who need robust type validation for user input, parsed data, regex matches, or any scenario where distinguishing numbers from non-numbers is critical.

Value Proposition

Developers choose is-number because it provides a performant, battle-tested solution that handles JavaScript's type coercion quirks consistently, reducing bugs and simplifying validation logic compared to manual checks.

Overview

JavaScript/Node.js utility. Returns true if the value is a number or string number. Useful for checking regex match results, user input, parsed strings, etc.

Use Cases

Best For

Validating user input from forms or APIs to ensure numeric values
Checking regex match results before mathematical operations
Parsing and validating data from external sources like CSV or JSON
Writing utility functions that require strict number type guards
Replacing error-prone manual checks with a reliable library
Ensuring consistent behavior across different JavaScript environments

Not Ideal For

Applications that require Infinity or NaN to be treated as valid numbers (e.g., scientific computing where infinite values are meaningful)
Projects where minimizing dependencies is paramount and inline checks with Number.isFinite suffice
TypeScript projects needing built-in type guards without external type definitions
Environments requiring broad type validation beyond numbers, as it only handles finite number detection

Pros & Cons

Pros

Robust Edge Case Handling

Correctly identifies tricky cases like +[] and +'' as non-numbers, avoiding false positives that naive casting methods produce, as highlighted in the README's examples.

Performance Optimized

Uses .isFinite internally and is 3x-4x faster for non-string/number values compared to previous versions, with benchmarks showing competitive speeds against parseFloat.

String Number Support

Recognizes numeric strings such as '5e3' and '0xff' as valid numbers, making it ideal for parsing user input or regex matches where type coercion is common.

Consistent Across Environments

Provides predictable results across different JavaScript runtimes, reducing bugs from inconsistent type checking in browsers or Node.js.

Cons

Breaking Changes History

Version 5.0.0 removed support for instanceof checks, and v7.0.0 introduced refactors, which could disrupt projects not carefully managing dependencies or updates.

Narrow Scope

Only checks for finite numbers; lacks features for validating integers, ranges, or other types, forcing developers to use additional libraries for comprehensive validation.

No Native TypeScript Support

The README doesn't mention TypeScript definitions, requiring users to rely on community-maintained types or manual declarations, adding setup overhead.

Frequently Asked Questions

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