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javascript/snippets/is-browser.md

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+---
+title: Environment is browser
+type: snippet
+tags: [browser]
+cover: travel-mug-3
+dateModified: 2020-10-20T23:02:01+03:00
+---
+
+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.prototype.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)
+```