Make is.number(NaN) return false (#90)

Co-authored-by: Sindre Sorhus <sindresorhus@gmail.com>

readme.md

@@ -68,6 +68,9 @@ All the below methods accept a value and returns a boolean for whether the value
 ##### .null(value)
 ##### .string(value)
 ##### .number(value)
+
+Note: `is.number(NaN)` returns `false`. This intentionally deviates from `typeof` behavior to increase user-friendliness of `is` type checks.
+
 ##### .boolean(value)
 ##### .symbol(value)
 ##### .bigint(value)
@@ -83,7 +86,7 @@ Keep in mind that [functions are objects too](https://developer.mozilla.org/en-U
 
 ##### .numericString(value)
 
-Returns `true` for a string that represents a number. For example, `'42'` and `'-8'`.
+Returns `true` for a string that represents a number satisfying `is.number`, for example, `'42'` and `'-8.3'`.
 
 Note: `'NaN'` returns `false`, but `'Infinity'` and `'-Infinity'` return `true`.
 

source/index.ts

@@ -117,7 +117,10 @@ const isObject = (value: unknown): value is object => typeof value === 'object';
 
 is.undefined = isOfType<undefined>('undefined');
 is.string = isOfType<string>('string');
-is.number = isOfType<number>('number');
+
+const isNumberType = isOfType<number>('number');
+is.number = (value: unknown): value is number => isNumberType(value) && !is.nan(value);
+
 is.bigint = isOfType<bigint>('bigint');
 
 // eslint-disable-next-line @typescript-eslint/ban-types

test/test.ts

@@ -493,7 +493,7 @@ test('is.string', t => {
 });
 
 test('is.number', t => {
-	testType(t, 'number', ['nan', 'integer', 'safeInteger', 'infinite']);
+	testType(t, 'number', ['integer', 'safeInteger', 'infinite']);
 });
 
 // TODO: Nodejs 10 only