diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index c1870cf..3b8aa86 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -10,12 +10,12 @@ jobs:
       fail-fast: false
       matrix:
         node-version:
+          - 16
           - 14
           - 12
-          - 10
     steps:
       - uses: actions/checkout@v2
-      - uses: actions/setup-node@v1
+      - uses: actions/setup-node@v2
         with:
           node-version: ${{ matrix.node-version }}
       - run: npm install
diff --git a/index.d.ts b/index.d.ts
index d760fa6..98c2236 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -1,3 +1,5 @@
+/* eslint-disable no-redeclare */
+
 declare namespace srcset {
 	interface SrcSetDefinition {
 		url: string;
@@ -5,7 +7,7 @@ declare namespace srcset {
 		density?: number;
 	}
 
-	interface SrcSetOptions {
+	interface Options {
 		/**
 		When strict mode is enabled, errors will be thrown on invalid input.
 
@@ -21,9 +23,9 @@ declare const srcset: {
 	/**
 	Parse the HTML `<img>` [srcset](http://mobile.smashingmagazine.com/2013/08/21/webkit-implements-srcset-and-why-its-a-good-thing/) attribute.
 
-	Accepts a srcset string and returns an array of objects with the possible properties: `url` (always), `width`, `density`, and `height`.
+	Accepts a “srcset” string and returns an array of objects with the possible properties: `url` (always), `width`, `density`, and `height`.
 
-	@param srcset - A srcset string.
+	@param srcset - A “srcset” string.
 
 	@example
 	```
@@ -42,14 +44,14 @@ declare const srcset: {
 	// ]
 	```
 	*/
-	parse: (srcset: string, options?: srcset.SrcSetOptions) => srcset.SrcSetDefinition[];
+	parse: (srcset: string, options?: srcset.Options) => srcset.SrcSetDefinition[];
 
 	/**
-	Stringify `SrcSetDefinition`s. Accepts an array of `SrcSetDefinition` objects and returns a srcset string.
+	Stringify `SrcSetDefinition`s.
 
-	@param SrcSetDefinitions - An array of `SrcSetDefinition` objects. Each object should have a `url` field and may have either `width` or `density`. When `options.strict` is set to false, a `height` field is also accepted, and multiple descriptors (`width`, `height`, and`density`) are accepted.
+	@param SrcSetDefinitions - Each object should have a `url` field and may have either `width` or `density`. When the `strict` option is `true`, only `width` or `density` is accepted.
 
-	@returns A srcset string.
+	@returns A “srcset” string.
 
 	@example
 	```
@@ -70,7 +72,7 @@ declare const srcset: {
 	// banner-HD.jpg 2x, banner-phone.jpg 100w
 	```
 	*/
-	stringify: (srcSetDefinitions: srcset.SrcSetDefinition[], options?: srcset.SrcSetOptions) => string;
+	stringify: (srcSetDefinitions: readonly srcset.SrcSetDefinition[], options?: srcset.Options) => string;
 };
 
 export = srcset;
diff --git a/index.js b/index.js
index 3d5b49a..2b0a40e 100644
--- a/index.js
+++ b/index.js
@@ -51,20 +51,32 @@ const validDescriptorCheck = (value, postfix, descriptor) => {
 		throw new TypeError(`${descriptor || value} is not a valid number`);
 	}
 
-	if (postfix === 'w') {
-		if (value <= 0) {
-			throw new Error('Width descriptor must be greater than zero');
-		} else if (!Number.isInteger(value)) {
-			throw new TypeError('Width descriptor must be an integer');
+	switch (postfix) {
+		case 'w': {
+			if (value <= 0) {
+				throw new Error('Width descriptor must be greater than zero');
+			} else if (!Number.isInteger(value)) {
+				throw new TypeError('Width descriptor must be an integer');
+			}
+
+			break;
+		}
+
+		case 'x': {
+			if (value <= 0) {
+				throw new Error('Pixel density descriptor must be greater than zero');
+			}
+
+			break;
 		}
-	} else if (postfix === 'x') {
-		if (value <= 0) {
-			throw new Error('Pixel density descriptor must be greater than zero');
+
+		case 'h': {
+			throw new Error('Height descriptor is no longer allowed');
+		}
+
+		default: {
+			throw new Error(`Invalid srcset descriptor: ${descriptor}`);
 		}
-	} else if (postfix === 'h') {
-		throw new Error('Height descriptor is no longer allowed');
-	} else {
-		throw new Error(`Invalid srcset descriptor: ${descriptor}`);
 	}
 };
 
@@ -90,12 +102,23 @@ exports.parse = (string, {strict = false} = {}) => {
 					duplicateDescriptorCheck(allDescriptors, value, postfix);
 				}
 
-				if (postfix === 'w') {
-					result.width = value;
-				} else if (postfix === 'h') {
-					result.height = value;
-				} else if (postfix === 'x') {
-					result.density = value;
+				switch (postfix) {
+					case 'w': {
+						result.width = value;
+						break;
+					}
+
+					case 'h': {
+						result.height = value;
+						break;
+					}
+
+					case 'x': {
+						result.density = value;
+						break;
+					}
+
+					// No default
 				}
 			}
 
@@ -127,12 +150,25 @@ exports.stringify = (array, {strict = false} = {}) => {
 		for (const descriptorKey of descriptorKeys) {
 			const value = element[descriptorKey];
 			let postfix;
-			if (descriptorKey === 'width') {
-				postfix = 'w';
-			} else if (descriptorKey === 'height') {
-				postfix = 'h';
-			} else if (descriptorKey === 'density') {
-				postfix = 'x';
+			switch (descriptorKey) {
+				case 'width': {
+					postfix = 'w';
+
+					break;
+				}
+
+				case 'height': {
+					postfix = 'h';
+
+					break;
+				}
+
+				case 'density': {
+					postfix = 'x';
+
+					break;
+				}
+			// No default
 			}
 
 			const descriptor = `${value}${postfix}`;
diff --git a/index.test-d.ts b/index.test-d.ts
index 7ccd92d..c105ee4 100644
--- a/index.test-d.ts
+++ b/index.test-d.ts
@@ -1,12 +1,10 @@
 import {expectType, expectError} from 'tsd';
-import srcset = require('.');
+import srcset = require('./index.js');
 
 const parsed = srcset.parse('banner-HD.jpg 2x, banner-phone.jpg 100w');
 expectType<srcset.SrcSetDefinition[]>(parsed);
 
-parsed.push({url: 'banner-phone-HD.jpg'});
-parsed.push({url: 'banner-phone-HD.jpg', width: 100});
-parsed.push({url: 'banner-phone-HD.jpg', density: 2});
+parsed.push({url: 'banner-phone-HD.jpg'}, {url: 'banner-phone-HD.jpg', width: 100}, {url: 'banner-phone-HD.jpg', density: 2});
 expectError(parsed.push({}));
 
 expectType<string>(srcset.stringify(parsed));
diff --git a/package.json b/package.json
index bf94be8..51a78ec 100644
--- a/package.json
+++ b/package.json
@@ -11,7 +11,7 @@
 		"url": "https://sindresorhus.com"
 	},
 	"engines": {
-		"node": ">=10"
+		"node": ">=12"
 	},
 	"scripts": {
 		"test": "xo && ava && tsd"
@@ -36,6 +36,6 @@
 	"devDependencies": {
 		"ava": "^2.4.0",
 		"tsd": "^0.13.1",
-		"xo": "^0.32.1"
+		"xo": "^0.39.0"
 	}
 }
diff --git a/readme.md b/readme.md
index 8608ac7..a419105 100644
--- a/readme.md
+++ b/readme.md
@@ -60,13 +60,13 @@ banner-HD.jpg 2x, banner-phone.jpg 100w, banner-super-HD.jpg 3x
 
 Parse the HTML `<img>` [srcset](http://mobile.smashingmagazine.com/2013/08/21/webkit-implements-srcset-and-why-its-a-good-thing/) attribute.
 
-Accepts a srcset string and returns an array of objects with the possible properties: `url` (always), `width`, `height`, and `density`.
+Accepts a “srcset” string and returns an array of objects with the possible properties: `url` (always), `width`, `height`, and `density`.
 
 #### string
 
 Type: `string`
 
-A srcset string
+A “srcset” string.
 
 #### options
 
@@ -74,21 +74,20 @@ Type: `object`
 
 ##### strict
 
-Type: `boolean`
-
+Type: `boolean`\
 Default: `false`
 
-Enable or disable validation of the srcset string. When enabled, an invalid srcset string will cause an error to be thrown. When disabled, a best effort will be made to parse the string, potentially resulting in invalid or nonsensical output.
+When enabled, an invalid “srcset” string will cause an error to be thrown. When disabled, a best effort will be made to parse the string, potentially resulting in invalid or nonsensical output.
 
 ### .stringify(SrcSetDefinitions, options?)
 
-Stringify `SrcSetDefinition`s. Accepts an array of `SrcSetDefinition` objects and returns a srcset string.
+Stringify `SrcSetDefinition`s. Accepts an array of `SrcSetDefinition` objects and returns a “srcset” string.
 
 #### srcsetDescriptors
 
 Type: `array`
 
-An array of `SrcSetDefinition` objects. Each object should have a `url` field and may have `width`, `height` or `density` fields. When `options.strict` is set to true, only `width` or `density` is permitted.
+An array of `SrcSetDefinition` objects. Each object should have a `url` field and may have `width`, `height` or `density` fields. When the `strict` option is `true`, only `width` or `density` is accepted.
 
 #### options
 
diff --git a/test.js b/test.js
index 5023c02..3fa0fb5 100644
--- a/test.js
+++ b/test.js
@@ -1,5 +1,5 @@
 import test from 'ava';
-import srcset from '.';
+import srcset from './index.js';
 
 test('.parse() should parse srcset', t => {
 	const fixture = ' banner-HD.jpeg 2x,    banner-phone.jpeg   100w, http://site.com/image.jpg?foo=bar,lorem 3x ,banner.jpeg    ';