Docs: add .astro Syntax guide (#137)
* wip: astro syntax docs * docs: update syntax guide * docs: add IDE note * chore: beautify file * docs: edits * Update docs/syntax.md Co-authored-by: Drew Powers <1369770+drwpow@users.noreply.github.com> * docs: be kinder to JSX :) * fix: spelling * docs: clarify some code comments Co-authored-by: Drew Powers <1369770+drwpow@users.noreply.github.com>
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docs/syntax.md
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docs/syntax.md
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## ✨ `.astro` Syntax
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"Yikes! Here we go again... They're really going to make me learn another new syntax?"
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Believe us, we know—and we wouldn't have introduced the `.astro` syntax without having some great reasons. Give us five minutes, read through this guide, and we think you'll be as excited about Astro as we are.
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---
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### Why use Astro?
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By focusing on HTML _instead of JavaScript_, Astro is able to be framework-agnostic.
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A common pain point for JavaScript newcomers is the ecosystem's steep learning curve. Choosing between build tools, frameworks, and meta frameworks is an enormous amount of work with long-term consequences. Not to mention that this all has to happen before you've written any code—much of which is just static markup.
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Astro's approach is based on the recognition that HTML is the lowest common denominator between frameworks. By using `.astro` as a composable, component-based format on top of HTML, you can start writing and styling your static content immediately.
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When you finally do need to introduce dynamic functionality, Astro allows you to _bring your own framework_, so you're free to use any component format you'd like without committing to a holistic architectural approach up-front. "The big question" is deferred until it actually needs to be answered.
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During a long-term project, you might even decide to switch frameworks somewhere down the road. Since Astro decouples decisions about data-loading and static rendering from your framework, that decision has a much smaller impact—try out the new framework on a single page or even mix both frameworks on some pages while you migrate.
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### What _are_ `.astro` files?
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If you're already familiar with **HTML or JSX**, you'll likely feel comfortable with `.astro` files right away.
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Think of `.astro` as **component-oriented HTML**. Components are reusable, self-contained blocks of HTML and CSS that belong together.
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```html
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<!-- This is a valid Astro component -->
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<html lang="en">
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<head>
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<meta charset="UTF-8" />
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<meta name="viewport" content="width=device-width, initial-scale=1.0" />
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<title>Document</title>
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</head>
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<body>
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<main>
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<h1>Hello world!</h1>
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</main>
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</body>
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</html>
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```
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```html
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<!-- This is also a valid Astro component! -->
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<main>
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<h1>Hello world!</h1>
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</main>
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```
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Developers have come up with a myriad of different techniques for composing blocks of HTML over the years, but far and away the most successful has been [JSX](https://reactjs.org/docs/introducing-jsx.html).
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We love JSX! In fact, `.astro` files borrow the highly-expressive templating syntax directly from JSX.
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```jsx
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<!-- This is an Astro component with expressions! -->
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<main>
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<h1>Hello {name}!</h1>
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<ul>
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{items.map((item) => (
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<li>{item}</li>
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))}
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</ul>
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</main>
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```
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`.astro` files also borrow the concept of [Frontmatter](https://jekyllrb.com/docs/front-matter/) from Markdown. Instead of introducing a new HTML-oriented `import` and `export` syntax, `.astro` just uses the JavaScript syntax you likely already know.
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```jsx
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---
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// This area is TypeScript (and therefore JavaScript)!
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import MyComponent from './MyComponent.astro'
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---
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<title>Document</title>
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</head>
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<body>
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<MyComponent></MyComponent>
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</body>
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</html>
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```
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### Data and Props
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`.astro` components can define local variables inside of the Frontmatter script. These are automatically exposed to the content below.
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```jsx
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---
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let name = 'world';
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---
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<main>
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<h1>Hello {name}!</h1>
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</main>
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```
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`.astro` components can also accept props when they are rendered. Public props can be marked using the `export` keyword.
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Local values are overwritten when props are passed, otherwise they are considered the default value.
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```jsx
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---
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export let greeting = 'Hello';
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export let name;
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---
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<main>
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<h1>{greeting} {name}!</h1>
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</main>
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```
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### `.astro` versus `.jsx`
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`.astro` files can end up looking very similar to `.jsx` files, but there are a few key differences. Here's a comparison between the two formats.
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| Feature | Astro | JSX |
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|------------------------- |------------------------------------------ |---------------------------------------------------- |
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| File extension | `.astro` | `.jsx` or `.tsx` |
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| User-Defined Components | `<Capitalized>` | `<Capitalized>` |
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| Expression Syntax | `{}` | `{}` |
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| Spread Attributes | `{...props}` | `{...props}` |
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| Boolean Attributes | `autocomplete` === `autocomplete={true}` | `autocomplete` === `autocomplete={true}` |
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| Inline Functions | `{items.map(item => <li>{item}</li>)}` | `{items.map(item => <li>{item}</li>)}` |
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| IDE Support | WIP - [VS Code][code-ext] | Phenomenal |
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| Requires JS import | No | Yes, `jsxPragma` (`React` or `h`) must be in scope |
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| Fragments | Automatic | Wrap with `<Fragment>` or `<>` |
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| Multiple frameworks per-file | Yes | No |
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| Modifying `<head>` | Just use `<head>` | Per-framework (`<Head>`, `<svelte:head>`, etc) |
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| Comment Style | `<!-- HTML -->` | `{/* JavaScript */}` |
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| Special Characters | ` ` | `{'\xa0'}` or `{String.fromCharCode(160)}` |
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| Attributes | `dash-case` | `camelCase` |
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### TODO: Styling
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### TODO: Composition (Slots)
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[code-ext]: https://marketplace.visualstudio.com/items?itemName=astro-build.astro
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