From 076d9ff8f252fefbf24f91c3c8b4ab9ec6e35496 Mon Sep 17 00:00:00 2001
From: Younho Choo <yo+github@younho9.com>
Date: Tue, 4 Jan 2022 07:51:36 +0900
Subject: [PATCH] Add `isInfinite()` (#29)

---
 readme.md             |  1 +
 source/index.ts       |  1 +
 source/is-infinite.ts | 10 ++++++++++
 test/is-infinite.ts   | 18 ++++++++++++++++++
 4 files changed, 30 insertions(+)
 create mode 100644 source/is-infinite.ts
 create mode 100644 test/is-infinite.ts

diff --git a/readme.md b/readme.md
index 67a4ad2..09bd3d7 100644
--- a/readme.md
+++ b/readme.md
@@ -30,6 +30,7 @@ import {isDefined} from 'ts-extras';
 - [`isDefined`](source/is-defined.ts) - Check whether a value is defined (not `null` or `undefined`).
 - [`isEmpty`](source/is-empty.ts) - Check whether an array is empty.
 - [`assertError`](source/assert-error.ts) - Assert that the given value is an `Error`.
+- [`isInfinite`](source/is-infinite.ts) - Check whether a value is infinite.
 
 **Improved builtin**
 
diff --git a/source/index.ts b/source/index.ts
index 0db1fd0..9521a09 100644
--- a/source/index.ts
+++ b/source/index.ts
@@ -4,6 +4,7 @@ export {assertError} from './assert-error.js';
 export {isDefined} from './is-defined.js';
 export {isEmpty} from './is-empty.js';
 export {isFinite} from './is-finite.js';
+export {isInfinite} from './is-infinite.js';
 export {isInteger} from './is-integer.js';
 export {isSafeInteger} from './is-safe-integer.js';
 export {objectEntries} from './object-entries.js';
diff --git a/source/is-infinite.ts b/source/is-infinite.ts
new file mode 100644
index 0000000..22d7d47
--- /dev/null
+++ b/source/is-infinite.ts
@@ -0,0 +1,10 @@
+import {NegativeInfinity, PositiveInfinity} from 'type-fest';
+
+/**
+Check whether a value is infinite.
+
+@category Type guard
+*/
+export function isInfinite(value: unknown): value is NegativeInfinity | PositiveInfinity {
+	return !Number.isNaN(value) && !Number.isFinite(value);
+}
diff --git a/test/is-infinite.ts b/test/is-infinite.ts
new file mode 100644
index 0000000..cb29219
--- /dev/null
+++ b/test/is-infinite.ts
@@ -0,0 +1,18 @@
+import test from 'ava';
+import {expectTypeOf} from 'expect-type';
+import {NegativeInfinity, PositiveInfinity} from 'type-fest';
+import {isInfinite} from '../source/index.js';
+
+test('isInfinite()', t => {
+	t.false(isInfinite(123));
+	t.true(isInfinite(Number.POSITIVE_INFINITY));
+	t.true(isInfinite(Number.NEGATIVE_INFINITY));
+
+	const number_ = 123 as number;
+
+	if (isInfinite(number_)) {
+		expectTypeOf<PositiveInfinity | NegativeInfinity>(number_);
+	} else {
+		expectTypeOf<number>(number_);
+	}
+});