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Returns true if the value is a finite number.

Please consider following this project’s author, Jon Schlinkert, and consider starring the project to show your :heart: and support.


Install with npm:

$ npm install --save is-number

Why is this needed?

In JavaScript, it’s not always as straightforward as it should be to reliably check if a value is a number. It’s common for devs to use +, -, or Number() to cast a string value to a number (for example, when values are returned from user input, regex matches, parsers, etc). But there are many non-intuitive edge cases that yield unexpected results:

console.log(+[]); //=> 0
console.log(+''); //=> 0
console.log(+'   '); //=> 0
console.log(typeof NaN); //=> 'number'

This library offers a performant way to smooth out edge cases like these.


const isNumber = require('is-number');

See the tests for more examples.


isNumber(5e3);               // true
isNumber(0xff);              // true
isNumber(-1.1);              // true
isNumber(0);                 // true
isNumber(1);                 // true
isNumber(1.1);               // true
isNumber(10);                // true
isNumber(10.10);             // true
isNumber(100);               // true
isNumber('-1.1');            // true
isNumber('0');               // true
isNumber('012');             // true
isNumber('0xff');            // true
isNumber('1');               // true
isNumber('1.1');             // true
isNumber('10');              // true
isNumber('10.10');           // true
isNumber('100');             // true
isNumber('5e3');             // true
isNumber(parseInt('012'));   // true
isNumber(parseFloat('012')); // true


Everything else is false, as you would expect:

isNumber(Infinity);          // false
isNumber(NaN);               // false
isNumber(null);              // false
isNumber(undefined);         // false
isNumber('');                // false
isNumber('   ');             // false
isNumber('foo');             // false
isNumber([1]);               // false
isNumber([]);                // false
isNumber(function () {});    // false
isNumber({});                // false

Release history


  • Refactor. Now uses .isFinite if it exists.
  • Performance is about the same as v6.0 when the value is a string or number. But it’s now 3x-4x faster when the value is not a string or number.


  • Optimizations, thanks to @benaadams.


Breaking changes

  • removed support for instanceof Number and instanceof String


As with all benchmarks, take these with a grain of salt. See the benchmarks for more detail.

# all
v7.0 x 413,222 ops/sec ±2.02% (86 runs sampled)
v6.0 x 111,061 ops/sec ±1.29% (85 runs sampled)
parseFloat x 317,596 ops/sec ±1.36% (86 runs sampled)
fastest is 'v7.0'

# string
v7.0 x 3,054,496 ops/sec ±1.05% (89 runs sampled)
v6.0 x 2,957,781 ops/sec ±0.98% (88 runs sampled)
parseFloat x 3,071,060 ops/sec ±1.13% (88 runs sampled)
fastest is 'parseFloat,v7.0'

# number
v7.0 x 3,146,895 ops/sec ±0.89% (89 runs sampled)
v6.0 x 3,214,038 ops/sec ±1.07% (89 runs sampled)
parseFloat x 3,077,588 ops/sec ±1.07% (87 runs sampled)
fastest is 'v6.0'


Contributing Pull requests and stars are always welcome. For bugs and feature requests, [please create an issue](../../issues/new).
Running Tests Running and reviewing unit tests is a great way to get familiarized with a library and its API. You can install dependencies and run tests with the following command: ```sh $ npm install && npm test ```
Building docs _(This project's is generated by [verb](, please don't edit the readme directly. Any changes to the readme must be made in the []( readme template.)_ To generate the readme, run the following command: ```sh $ npm install -g verbose/verb#dev verb-generate-readme && verb ```

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Commits Contributor
49 jonschlinkert
5 charlike-old
1 benaadams
1 realityking


Jon Schlinkert


Copyright © 2018, Jon Schlinkert. Released under the MIT License.

This file was generated by verb-generate-readme, v0.6.0, on June 15, 2018.