20 lines
789 B
Markdown
20 lines
789 B
Markdown
---
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title: isBrowser
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tags: browser,node,intermediate
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---
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Determines if the current runtime environment is a browser so that front-end modules can run on the server (Node) without throwing errors.
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- 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`.
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- `typeof` allows globals to be checked for existence without throwing a `ReferenceError`.
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- If both of them are not `undefined`, then the current environment is assumed to be a browser.
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```js
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const isBrowser = () => ![typeof window, typeof document].includes('undefined');
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```
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```js
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isBrowser(); // true (browser)
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isBrowser(); // false (Node)
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```
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