Merge branch 'master' into observable-improvement

package.json

@@ -49,7 +49,7 @@
 		"@types/node": "^10.12.10",
 		"@types/tempy": "^0.2.0",
 		"@types/zen-observable": "^0.8.0",
-		"ava": "*",
+		"ava": "^0.25.0",
 		"del-cli": "^1.1.0",
 		"jsdom": "^11.6.2",
 		"rxjs": "^6.3.3",

readme.md

@@ -255,6 +255,22 @@ is.urlInstance(url);
 //=> true
 ```
 
+### .url(value)
+
+Returns `true` if `value` is a URL string.
+
+Note: this only does basic checking using the [`URL` class](https://developer.mozilla.org/en-US/docs/Web/API/URL) constructor.
+
+```js
+const url = 'https://example.com';
+
+is.url(url);
+//=> true
+
+is.url(new URL(url));
+//=> false
+```
+
 ##### .truthy(value)
 
 Returns `true` for all values that evaluate to true in a boolean context:

source/index.ts

@@ -2,6 +2,7 @@
 /// <reference lib="es2017.sharedmemory"/>
 /// <reference lib="esnext.asynciterable"/>
 /// <reference lib="dom"/>
+import {URL} from 'url';
 
 type TypedArray = Int8Array | Uint8Array | Uint8ClampedArray | Int16Array | Uint16Array | Int32Array | Uint32Array | Float32Array | Float64Array;
 type Primitive = null | undefined | string | number | boolean | Symbol;
@@ -188,6 +189,19 @@ namespace is { // tslint:disable-line:no-namespace
 	export const directInstanceOf = <T>(instance: unknown, klass: Class<T>): instance is T => Object.getPrototypeOf(instance) === klass.prototype;
 	export const urlInstance = (value: unknown): value is URL => isObjectOfType<URL>(TypeName.URL)(value);
 
+	export const urlString = (value: unknown) => {
+		if (!string(value)) {
+			return false;
+		}
+
+		try {
+			new URL(value); // tslint:disable-line no-unused-expression
+			return true;
+		} catch {
+			return false;
+		}
+	};
+
 	export const truthy = (value: unknown) => Boolean(value);
 	export const falsy = (value: unknown) => !value;
 

source/tests/test.ts

@@ -576,13 +576,22 @@ test('is.directInstanceOf', t => {
 });
 
 test('is.urlInstance', t => {
-	const url = new URL('https://www.example.com');
+	const url = new URL('https://example.com');
 	t.true(is.urlInstance(url));
 	t.false(is.urlInstance({}));
 	t.false(is.urlInstance(undefined));
 	t.false(is.urlInstance(null));
 });
 
+test('is.urlString', t => {
+	const url = 'https://example.com';
+	t.true(is.urlString(url));
+	t.false(is.urlString(new URL(url)));
+	t.false(is.urlString({}));
+	t.false(is.urlString(undefined));
+	t.false(is.urlString(null));
+});
+
 test('is.truthy', t => {
 	t.true(is.truthy('unicorn'));
 	t.true(is.truthy('🦄'));
@@ -681,8 +690,9 @@ test('is.class', t => {
 });
 
 test('is.typedArray', t => {
-	// Typescript currently does not support empty constructors for these
+	// TypeScript currently does not support empty constructors for these
 	// See https://github.com/Microsoft/TypeScript/issues/19680
+	// TODO: Remove the `0` when targeting `es2017` (Node.js 8), in other places of this file too.
 	const typedArrays = [
 		new Int8Array(0),
 		new Uint8Array(0),