Create isBrowser.md

snippets/isBrowser.md

@@ -0,0 +1,19 @@
+### isBrowser
+
+Determines if the current runtime environment is a browser so that front-end modules can run on the server (Node)
+without throwing errors.
+
+Use `Array.includes()` on the `typeof` values of both `window` and `document` (globals usually only available in a 
+browser environment unless they were explicitly defined), which will return `true` if one of them is `undefined`. 
+`typeof` allows globals to be checked for existence without throwing a ReferenceError.
+
+If both of them are not `undefined`, then the current environment is assumed to be a browser.
+
+```js
+const isBrowser = () => ![typeof window, typeof document].includes('undefined')
+```
+
+```js
+isBrowser() // true (browser)
+isBrowser() // false (Node)
+```