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preact-helmet

Preact Helmet

A document head manager for Preact

This project is a port of react-helmet to Preact, the 3kB lightweight React alternative.

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This Preact component will manage all of your changes to the document head with support for document title, meta, link, style, script, noscript, and base tags.

Inspired by:

Table of Contents generated with DocToc

Examples

import {h} from "preact"; /** @jsx h */
import Helmet from "preact-helmet";
 
export default function Application () {
    return (
        <div className="application">
            <Helmet title="My Title" />
            ...
        </div>
    );
};
import {h} from "preact"; /** @jsx h */
import Helmet from "preact-helmet";
 
export default function Application () {
    return (
        <div className="application">
            <Helmet
                htmlAttributes={{lang: "en", amp: undefined}} // amp takes no value 
                title="My Title"
                titleTemplate="MySite.com - %s"
                defaultTitle="My Default Title"
                titleAttributes={{itemprop: "name", lang: "en"}}
                base={{target: "_blank", href: "http://mysite.com/"}}
                meta={[
                    {name: "description", content: "Helmet application"},
                    {property: "og:type", content: "article"}
                ]}
                link={[
                    {rel: "canonical", href: "http://mysite.com/example"},
                    {rel: "apple-touch-icon", href: "http://mysite.com/img/apple-touch-icon-57x57.png"},
                    {rel: "apple-touch-icon", sizes: "72x72", href: "http://mysite.com/img/apple-touch-icon-72x72.png"}
                ]}
                script={[
                    {src: "http://include.com/pathtojs.js", type: "text/javascript"},
                    {type: "application/ld+json", innerHTML: `{ "@context": "http://schema.org" }`}
                ]}
                noscript={[
                    {innerHTML: `<link rel="stylesheet" type="text/css" href="foo.css" />`}
                ]}
                style={[
                  {type: "text/css", cssText: "body {background-color: blue;} p {font-size: 12px;}"}
                ]}
                onChangeClientState={(newState) => console.log(newState)}
            />
            ...
        </div>
    );
};

Features

  • Supports title, base, meta, link, script, noscript, and style tags.
  • Attributes for html and title tags.
  • Supports isomorphic/universal environment.
  • Nested components override duplicate head changes.
  • Duplicate head changes preserved when specified in same component (support for tags like "apple-touch-icon").
  • Callback for tracking DOM changes.

Installation

npm install --save preact-helmet

Server Usage

To use on the server, call rewind() after using render from preact-render-to-string to get the head data for use in your prerender.

Because this component keeps track of mounted instances, you have to make sure to call rewind on server, or you'll get a memory leak.

import { render } from 'preact-render-to-string'
import Helmet from 'preact-helmet'
 
const markup = renderToString(<MyApp />);
const head = Helmet.rewind();
 
// populate some document template using `markup` and `head` 
const html = `
    <!doctype html>
    <html>
        <head>
            ${head.title.toString()}
            ${head.meta.toString()}
            ${head.link.toString()}
        </head>
        <body>
            <div id="content">
                ${markup}
            </div>
        </body>
    </html>
`;
 

head contains the following properties:

  • htmlAttributes
  • title
  • base
  • meta
  • link
  • script
  • noscript
  • style

Each property contains toComponent() and toString() methods. Use whichever is appropriate for your environment. For htmlAttributes, use the JSX spread operator on the object returned by toComponent(). E.g:

As string output

const html = `
    <!doctype html>
    <html ${head.htmlAttributes.toString()}>
        <head>
            ${head.title.toString()}
            ${head.meta.toString()}
            ${head.link.toString()}
        </head>
        <body>
            <div id="content">
                ${markup}
            </div>
        </body>
    </html>
`;

As Preact components

If you are doing server side rendering with Preact, it may be easier to render the document template with Preact as well:

function HTML({head}) {
    const attrs = head.htmlAttributes.toComponent();
 
    return (
        <html {...attrs}>
            <head>
                {head.title.toComponent()}
                {head.meta.toComponent()}
                {head.link.toComponent()}
            </head>
            <body>
                <div id="content">
                    <MyApp />
                </div>
            </body>
        </html>
    );
}

Use Cases

  1. Nested or latter components will override duplicate changes.
<Helmet
    title="My Title"
    meta={[
        {"name": "description", "content": "Helmet application"}
    ]}
/>
<Helmet
    title="Nested Title"
    meta={[
        {"name": "description", "content": "Nested component"}
    ]}
/>

Yields:

<head>
    <title>Nested Title</title>
    <meta name="description" content="Nested component">
</head>
  1. Use a titleTemplate to format title text in your page title
<Helmet
    title="My Title"
    titleTemplate="%s | MyAwesomeWebsite.com"
/>
<Helmet
    title="Nested Title"
/>

Yields:

<head>
    <title>Nested Title | MyAwesomeWebsite.com</title>
</head>
  1. Duplicate meta and/or link tags in the same component are preserved
<Helmet
    link={[
        {"rel": "apple-touch-icon", "href": "http://mysite.com/img/apple-touch-icon-57x57.png"},
        {"rel": "apple-touch-icon", "sizes": "72x72", "href": "http://mysite.com/img/apple-touch-icon-72x72.png"}
    ]}
/>

Yields:

<head>
    <link rel="apple-touch-icon" href="http://mysite.com/img/apple-touch-icon-57x57.png">
    <link rel="apple-touch-icon" sizes="72x72" href="http://mysite.com/img/apple-touch-icon-72x72.png">
</head>
  1. Duplicate tags can still be overwritten
<Helmet
    link={[
        {"rel": "apple-touch-icon", "href": "http://mysite.com/img/apple-touch-icon-57x57.png"},
        {"rel": "apple-touch-icon", "sizes": "72x72", "href": "http://mysite.com/img/apple-touch-icon-72x72.png"}
    ]}
/>
<Helmet
    link={[
        {"rel": "apple-touch-icon", "href": "http://mysite.com/img/apple-touch-icon-180x180.png"}
    ]}
/>

Yields:

<head>
    <link rel="apple-touch-icon" href="http://mysite.com/img/apple-touch-icon-180x180.png">
</head>
  1. Only one base tag is allowed
<Helmet
    base={{"href": "http://mysite.com/"}}
/>
<Helmet
    base={{"href": "http://mysite.com/blog"}}
/>

Yields:

<head>
    <base href="http://mysite.com/blog">
</head>
  1. defaultTitle will be used as a fallback when the template does not want to be used in the current Helmet
<Helmet
    defaultTitle="My Site"
    titleTemplate="My Site - %s"
/>

Yields:

<head>
    <title>My Site</title>
</head>

But a child route with a title will use the titleTemplate, giving users a way to declare a titleTemplate for their app, but not have it apply to the root.

<Helmet
    defaultTitle="My Site"
    titleTemplate="My Site - %s"
/>
 
<Helmet
    title="Nested Title"
/>

Yields:

<head>
    <title>My Site - Nested Title</title>
</head>

And other child route components without a Helmet will inherit the defaultTitle.

  1. Usage with <script> tags:
<Helmet
    script={[{
        "type": "application/ld+json",
        "innerHTML": `{
            "@context": "http://schema.org",
            "@type": "NewsArticle"
        }`
    }]}
/>

Yields:

<head>
    <script type="application/ld+json">
      {
          "@context": "http://schema.org",
          "@type": "NewsArticle"
      }
    </script>
</head>
  1. Usage with <style> tags:
<Helmet
    style={[{
        "cssText": `
            body {
                background-color: green;
            }
        `
    }]}
/>

Yields:

<head>
    <style>
        body {
            background-color: green;
        }
    </style>
</head>

Contributing to this project

Please take a moment to review the guidelines for contributing.

License

MIT

More Examples

react-helmet-example (for React, but still useful)