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# react-helmet-async
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[](https://circleci.com/gh/staylor/react-helmet-async)
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[Announcement post on Times Open blog](https://open.nytimes.com/the-future-of-meta-tag-management-for-modern-react-development-ec26a7dc9183)
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This package is a fork of [React Helmet](https://github.com/nfl/react-helmet).
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`<Helmet>` usage is synonymous, but server and client now requires `<HelmetProvider>` to encapsulate state per request.
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`react-helmet` relies on `react-side-effect`, which is not thread-safe. If you are doing anything asynchronous on the server, you need Helmet to encapsulate data on a per-request basis, this package does just that.
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## Usage
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**New is 1.0.0:** No more default export! `import { Helmet } from 'react-helmet-async'`
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The main way that this package differs from `react-helmet` is that it requires using a Provider to encapsulate Helmet state for your React tree. If you use libraries like Redux or Apollo, you are already familiar with this paradigm:
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```javascript
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import React from 'react';
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import ReactDOM from 'react-dom';
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import { Helmet, HelmetProvider } from 'react-helmet-async';
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const app = (
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<HelmetProvider>
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<App>
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<Helmet>
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<title>Hello World</title>
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<link rel="canonical" href="https://www.tacobell.com/" />
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</Helmet>
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<h1>Hello World</h1>
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</App>
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</HelmetProvider>
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);
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ReactDOM.hydrate(
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app,
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document.getElementById(‘app’)
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);
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```
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On the server, we will no longer use static methods to extract state. `react-side-effect`
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exposed a `.rewind()` method, which Helmet used when calling `Helmet.renderStatic()`. Instead, we are going
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to pass a `context` prop to `HelmetProvider`, which will hold our state specific to each request.
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```javascript
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import React from 'react';
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import { renderToString } from 'react-dom/server';
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import { Helmet, HelmetProvider } from 'react-helmet-async';
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const helmetContext = {};
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const app = (
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<HelmetProvider context={helmetContext}>
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<App>
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<Helmet>
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<title>Hello World</title>
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<link rel="canonical" href="https://www.tacobell.com/" />
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</Helmet>
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<h1>Hello World</h1>
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</App>
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</HelmetProvider>
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);
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const html = renderToString(app);
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const { helmet } = helmetContext;
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// helmet.title.toString() etc…
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```
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## Streams
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This package only works with streaming if your `<head>` data is output outside of `renderToNodeStream()`.
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This is possible if your data hydration method already parses your React tree. Example:
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```javascript
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import through from 'through';
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import { renderToNodeStream } from 'react-dom/server';
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import { getDataFromTree } from 'react-apollo';
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import { Helmet, HelmetProvider } from 'react-helmet-async';
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import template from 'server/template';
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const helmetContext = {};
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const app = (
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<HelmetProvider context={helmetContext}>
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<App>
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<Helmet>
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<title>Hello World</title>
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<link rel="canonical" href="https://www.tacobell.com/" />
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</Helmet>
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<h1>Hello World</h1>
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</App>
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</HelmetProvider>
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);
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await getDataFromTree(app);
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const [header, footer] = template({
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helmet: helmetContext.helmet,
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});
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res.status(200);
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res.write(header);
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renderToNodeStream(app)
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.pipe(
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through(
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function write(data) {
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this.queue(data);
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},
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function end() {
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this.queue(footer);
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this.queue(null);
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}
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)
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)
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.pipe(res);
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```
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## Usage in Jest
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While testing in using jest, if there is a need to emulate SSR, the following string is required to have the test behave the way they are expected to.
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```
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import { HelmetProvider } from 'react-helmet-async';
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HelmetProvider.canUseDOM = false;
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```
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## License
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Licensed under the Apache 2.0 License, Copyright © 2018 Scott Taylor
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