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What is Elegua?

Elegua: the best Svelte micro client router you'll ever see.

Small example

It's hopefully very straighforward: there are no components, just some stores reflecting current path/parts of url, and a resolve() function for more complex (regexp/named routes) routings. The rest is just your plain Svelte logical blocks.

{#if $path === '/'}
  <h1>Home page</h1>
{:else if $path === '/about'}
  <h1>About page</h1>
{:else if resolve($path, '/blog/:slug')}
  <Post slug={$params('slug')}/>
{:else}
  <h1>404</h1>
  <p>Not found: {$path}</p>
{/if}

Demo

Online: https://elegua.netlify.app/

... or run yourself:

git clone http://github.com/howesteve/elegua
cd elegua
pnpm install
pnpm run dev

Features

Why?

Homepage

http://github.com/howesteve/elegua

About this repository

Most of this repository is a demo applicaion for Elegua. But Elegua itself is a single file.

Documentation

You mean, besides reading the source code? :) Here it goes.

Install

pnpm

pnpm i -D elegua

npm

npm i -D elegua

yarn

yarn i -D elegua

Usage

Elegua's routing is designed expecting routes are mainly guided by path, of course. However, you can route by hash, searchParams, url or anything else you want.

Every time the current browser's url changes, Elegua will update its stores and your routing logic will do the rest.

:warning: WARNING: It's best to define routes in your main application's page and not in subpages that are lazily loaded, otherwise routes might not be defined when you think they are, and that could lead to unexpected results.

A more comprehensive example of how routing looks like in Elegua:

<script lang="ts">
  import { path, resolve, params, match } from 'elegua';
</script>

<main>
  <!-- Simple main page route -->
  {#if $path === '/'}
    <Home />
    <!-- /about - another static route. -->
  {:else if $path === '/about'}
    <About />
    <!-- Nested paths routing - you can use any path -->
  {:else if $path === '/blog/main-post'}
    <MainBlogPost />
    <!-- Static page resolving using resolve() function -->
  {:else if resolve($path, '/users')}
    <Users />
    <!-- Named param: $match will have the matching param "slug" -->
  {:else if resolve($path, '/blog/:slug')}
    <PostPage slug={$match['slug']} />
    <!-- Multiple named paths: $match will have all the matching params -->
  {:else if resolve($path, '/blog/:author/:slug')}
    <PostPage author={$params['author']} slug={$params['slug']} />
    <!-- RegExp route: $match will have the matching params, same as with named paths -->
  {:else if resolve($path, /\/authors\/([0-9]+)/)}
    <Author id={$match[1]} />
  {:else}
    <!-- Fallback/error route "*" - this will get matched/rendered if nothing else did. You can inspect $path, $url, etc as usual to see what user tried to reach -->
    <Error />
  {/if}
</main>

Methods

resolve()

resolve(path: string, route: string|RegExp)

The resolve(path, route) function is Elegua's core route resolver. It accepts plain string, named or regExp route param, and while in a template block, it's designed to be used with the $path argument to be called reactively whenever the url changes

See below for examples:

<!-- fixed route -->
{#if resolve($path, '/')}
  <h1>Home page</h2>
<!-- named params route -->
{:else if resolve($path, '/blog/:post_id')}
  <Post id={$params["post_id"]}/>
<!-- regexp route -->
{:else if resolve($path, /users\/([a-zA-Z])+/)}
  <p>This is the page for user {$match[1]}
{:else}
  <!-- None of the above matched? Render the error route -->
  <h1>Error 404</h1>
  <p>Page {$path} not found</p>
{/if}

Note

Implementation detail. One might wonder why I left a $path param in the resolve(path, route) api - it might seem cumbersome, why not using just resolve('/')? It's because otherwise Svelte wouldn't know it has to re-render the template containing the resolve block. With $path explicitly appearing in template block, Svelte will re-render it every time $path changes, and resolve() gets called. Otherwise, path changes would not be perceived.

goto()

goto(href: string|URL)

The goto(href) method navigates to some url/path programmatically. Internally, it uses history.pushState(). Calls to goto(href) will trigger updates in all the expected reactive stores: $path, $url, $hash, $oldUrl, etc. - and also will update the current browser's url.

preventChange()

preventChange : (()=> boolean|undefined) | undefined

This function allows setting a callback for preventing exiting a route/page from either clicking <a> links or using goto(). If the callback function returns true, the link change will be blocked. If it returns anything else, it will be allowed. For instance, for preventing going away from a form has been changed:

preventChange(() => {
  if (formIsDirty) {
    alert('Please save or cancel changes before navigating away.');
    return true;
  }
});

To unset the callback, just call preventChange() without arguments:

preventChange()

For a more useful example of calling preventChange() inside the onMount()/onDestroy() handlers, check our demo app and it's source.

Note

This method will not prevent the user from closing the window/reloading the page. That is accomplished by handiling the beforeload event. But check the preventUnload action for a nice wrapper.

I don't know of any other routers that have this feature.

preventUnload()

preventUnload(callback: () => boolean | string| undefined)

This is a svelte action that will prevent the user from closing the current window if a condition is met. It can be used in set with preventChange to prevent the user from closing or navigating away from the changed forms.

<svelte:window use:preventUnload={() => formIsdirty()} />
...
</svelte:window>

Although this is not a part of the routing system per se, I think it's a nice addition to Elegua. Same as with preventChange, I don't know about any other routers that have this feature.

dynamic()

dynamic(path: string, routes: DynamicRoute[], defaultRoute?: ComponentType): ComponentType|undefined type DynamicRoute = [string | RegExp, ComponentType, any?]

The dynamic() method is a very special one; it allows dynamic routing using Elegua:

<script lang="ts">
  import {dynamic} from 'elegua';
  import Home from './Home.svelte';
  import About from './About.svelte';
  import Blog from './Blog.svelte';
  import Error from './Error404.svelte';
</script> 

<svelte:component this={dynamic($path, [
  ['/', Home],
  ['/about', About],
  ['/blog', Blog],
  ['/blog/:post', Post],
], Error)} />

Sometimes you might have a lot of static routes that point to components and don't want to define them one by one in {$if} blocks, or you just don't know the routes beforehand. For such cases, dynamic() is very handy.

The arguments are:

If you need to inspect any Elegua variables inside your dynamically rendered component, please do it from inside the component. For instance, in the example above, the Post component could be implemented as:

<p>This is post id {$params["post"]}</p>

or:

<script>
  onMount(()=> {
    if ($params['post']) {
      <!-- Load post from server -->
    }
  })
</script>

Stores

$path

A writable store that reflects the current url's path. If you load http://localhost/blog, $path will be set as "/blog". If you set $path using path.set("/") or $path = "/", it will update the value store and the browser will load home route (similar to using goto("/")).

This is used very often for simple, fixed routings.

<script lang="ts">
  import { path } from 'elegua';
</script>

<h1>Your are now in the {$path} page.</h1>
<p>Set path:</p>
<button on:click|preventDefault={() => ($path = '/blog')}>Set $path='/blog'</button>

Use Svelte's {#if} blocks for routing using $path:

<script lang="ts">
  import { path } from 'elegua';
  import Home from './Home.svelte';
  import Blog from './Blog.svelte';
</script>

{#if $path === '/'}
  <Home />
{:else if $path === '/blog'}
  <Blog />
{/if}

Note

Routing using $path as stated above (e.g.$path === '/blog') works fine, but $match and $params will be unchanged and might be reflecting the values from the latest previous resolve() call. If that's not what you want, route static paths using resolve():

<script lang="ts">
  import { path } from 'elegua';
</script>

{#if resolve($path, '/')}
  <h1>Home page. {$match} and {$params} are empty.</h1>
{/if}

$url

This writable store is a URL object for the current loaded url. Anytime the browser's url changes, $url will be updated. And if you update $url, the current browser's url will change to reflect it as well. You can inspect/use url.pathname, url.hash, url.searchParams, etc.

<script lang="ts">
  import { url } from 'elegua';
</script>

Current page: {$url.pathname}
<br />Current path: {$url.pathname}
<br />Current hash: {$url.hash}
<br />Current searchParams: {$url.searchParams}

Using $url, you can handle any kind of routing. For instance, loading a post by hash using $url:

<script lang="ts">
  import { url } from 'elegua';
  let post: Post;
  url.subscribe(async (u) => {
    // Loading post by hash
    post = await getPost(u.hash);
  });
</script>

<Post data={post} />

$hash

A writable store that reflects the current url's hash. If you load http://localhost/#xxx, $hash will be set as "xxx". If you call hash.set('xxx'), $hash will be set to 'xxx', and the browser url will be updated.

Important

Elegua strips the # symbol is from the hash string, i.e. on url http://localhost/blog#myhash, $hash will be myhash instead of #myhash.

<script lang="ts">
  import Router, { hash } from 'elegua';
</script>

<h1>The current hash is: {$hash}</h1>

Internally, it works by monitoring both popstate and hashchange events.

$searchParams

This readable store is a URLSearchParams object for the current url. For instance, if you load:http://localhost/blog?x=1 and call $searchParams.get('x'), you'll get "1" (yes, a string). For changing a searchParams value, call $searchParams.set("x", "1"). Check the URLSearchParams reference for other methods.

Elegua has reactive searchParams.set() and searchParams.delete() and searchParams.append()methods for convenience; if you use them, the current browser's url and history will automatically be updated, and if you change the url values, searchParams will reflect them.

Reading from searchParams:

<script lang="ts">
  import { searparams } from 'elegua';
</script>

{#if resolve($path, '/blog')}
  <!-- when you load /blog/searchparams?x=1-->
  Param <code>x</code> is {$searchParams.get('x')}.
  <br />(should print "1")
{/if}

Routing using searchParams:

<script lang="ts">
  import { searparams } from 'elegua';
</script>

<!-- when you load, ex /blog?x=1-->
{@const x = $searchParams.get('x')}
{#if x === 1}
  Param <code>x</code> is 1.
{:else if x === 2}
  Param <code>x</code> is 2.
{:else}
  Param <code>x</code> is {x}.
{/if}
<br />(should print "1")

Setting a searchParam (reactive - browser url will change):

<button
  on:click|preventDefault={() => {
    $searchParams.set('x', '1');
  }}>Set x</button
>

Removing a searchParam (reactive - browser url will change):

<button
  on:click|preventDefault={() => {
    $searchParams.delete('x');
  }}>Remove x</button
>

Appending a searchParam (reactive - browser url will change):

<button
  on:click|preventDefault={() => {
    $searchParams.append('y', 1);
  }}>Append('y', 1)</button
>

Multiple searchParam changes

These helper $searchParam methods above perform both the searchParam update and a history push at the same time. I implemented this way to make the most common case, i.e. single searchParam updates, easier. They call $url.searchParams.xxx() internally. But somethimes, you might want to change multiple searchParam and do a single history push for them all after those changes, avoiding ending up with a lot of history items for every change. For that, use the original $url.searchParams.xxx() methods for each change, and "commit" them all at once at the end by calling goto:

// do all changes you want using original URL.searchParams methods
$url.searchParams.set('a', 1);
$url.searchParams.set('b', 2);
$url.searchParams.append('c', 3);
 //(...) 
// then push all above changes into history just once
goto($url)

Note searchParam.append() will perform exactly as URLSearchParam.append(), i.e. if you call it multiple times, it will append params multiple times.

$match

This readable store will be set after a resolve(path, route) call. If the route is a regexp route, match[x] will have all matching results.

$match is just the return from the regexp.exec().groups() called internally to resolve the route - so, it's number indexed. For instance, when loading http://localhost/blog/my-post or http://localhost/users/my-user

<script lang="ts">
  import { matches } from 'elegua';
</script>

{#if resolve($path, '/blog/:slug')}
  Blog post {match[1]} (="my-post")
{:else if resolve($path, /users\/([a-zA-Z\-])+/)}
  User: {match[1]} (="my-user")
{/if}

Important

$match is only updated after a resolve() call. Specifically, $path-based routing will not update this store.

$params

This store contains the named (variable) parts of a match, after a resolve call; is kinda similar to $match, but whereas $match is indexed by number, $params expects strings.

<script lang="ts">
  import { params } from 'elegua';
</script>

{#if resolve($path, '/blog/:slug')}
  You are rendering the {$params['slug']} blog post.
{/if}

$params will also have any regexp named groups:

<script lang="ts">
  import { params } from 'elegua';
</script>

{#if resolve($path, /\/blog\/(?<slug>[a-zA-Z0-9]+)/)}
  You are rendering the {$params['slug']} blog post.
{/if}

Important

Just as with $match, $params is only updated after a resolve() call. Specifically, $path-based routing will not update these stores.

$oldUrl

A store for the old (previous) url before the last change.

<script lang="ts">
  import { path, oldUrl } from 'elegua';
</script>

<h1>Your are now in the {$path} page, coming from {$oldUrl.pathname}.</h1>

Howto's/Recipes/FAQ

How to start a project from scratch

$ pnpm create vite@latest elegua-test --template svelte
$ cd elegua-test
$ pnpm install -D elegua

Then, edit src/App.svelte (i.e. "code ." if you use vscode) and replace it with something like:

<script>
  import { path } from "elegua";
</script>

<header>
  <nav>
    <ul id="menu">
      <li><a href="/" class:selected={$path === "/"}>Home</a></li>
      <li><a href="/about" class:selected={$path === "/about"}>About</a></li>
    </ul>
  </nav>
</header>

<main>
  {#if $path === "/"}
    <h1>Home page</h1>
  {:else if $path === "/about"}
    <h1>About page</h1>
  {:else}
    <h1>Error 404</h1>
    <p>Not found</p>
  {/if}
</main>

<style>
  a {
    text-decoration: none;
  }
  a:hover {
    text-decoration: underline;
  }
  a:visited {
    color: inherit;
  }
  .selected {
    font-weight: bolder;
  }
  ul#menu li {
    display: inline;
    margin-right: 1em;
  }
  header {
    font-size: large;
  }
</style>

Fallback route/404/error page

Just use regular Svelte if blocks. When nothing else matches, show your error page.

<script lang="ts">
  import { path } from 'elegua';
</script>

{#if $path === '/'}
  <h1>Home page</h1>
{:else}
  <p>No such path: {$path}</p>
{/if}

Named routes

Named routes are routes that can have named variables, prefixed with ":", such as /blog/:slug:

<script lang="ts">
  import { resolve } from 'elegua';
</script>

{#if resolve('/blog/:slug')}
  <Post id={$params['slug']} />
{/if}

The $params store will reflect the params by name. Internally, this is implemented using a RegExp route.

If the last resolve() call did not use named routes/or regexp matching (i.e. a hash match), $params will be empty.

A named route will resolve with any string. If you need more control of what's matched by a named route, you should either be using regexp routes or a more specialized subrouting:

<script lang="ts">
  import { resolve } from 'elegua';
</script>

{#if resolve('/blog/:slug')}
  {#if $params['slug'] == "1"}
    <Post1/>
  {:else if $params['slug'] == "2"}
    <Post2/>
  {:else if $params['slug'] == "3"}
    <Post3/>
  {:else}  
    <h1>Post not found</h1>
  {/if}
{/if}

Regexp routes

If you might want a route to match only on certain specific path patterns; ex: /users/123. For that, use regexp routes by passing a regexp as route in the resolve(path, route) method:

{#if resolve($path, /\/users/([0-9]+)/)}
  <p>Rendering user {$match[1]} page</p>
{/if}

You could use other patterns in the same way. Ex:

Named groups work as expected, and captured groups will be reflected in $params. After (and only after ) resolve() is called, $match and $params will be redefined.

{#if resolve($path, /users\/(?<user_id>[0-9]+)/)}
  <p>User by $match: {$match && $match[1]}</p>
  <p>User by $param: {$param['user_id']}</p>
{/if}

Nav menu highlighting

Often you want to highlight a nav menu item when user is on that page, so that he can see at a glance where they are. For instance, if you are in "/about" and your nav menu has the following links:

BLOG | ORDERS | ABOUT

... and you want ABOUT highlighted when user is on that page (/about). In this case, just set a dynamic class inspecting $path:

<script lang="ts">
  import { path } from 'elegua';
</script>

<nav>
  <a href={'/blog'} class:selected={$path === '/blog' || $path.startsWith('/blog/')}>BLOG </a>
  <a href={'/orders'} class:selected={$path === '/orders'}>ORDERS </a>
  <a href={'/about'} class:selected={$path === '/about'}>ABOUT </a>
</nav>

<style>
  .selected {
    font-weight: bold;
  }
</style>

Now when you are on /about, nav menu will show something as:

<code>BLOG | ORDERS | <b>ABOUT</b></code>

How do I handle any other kind of url changes?

Subscribe to $url. It's the DOM URL object for the current browser's url. Then you can do anything you want with it.

Redirects

No need to bloat Elegua with that. Just use <meta refresh="url...">:

<script lang="ts">
  import { path } from 'elegua';
</script>

{#if $path ==="/old_blog"}
  <svelte:head>
    <meta http-equiv="refresh" content="3; url = /blog"/>
  </sve
  Blog has changed path; redirecting...
{/if}

goto() is another way to do it:

<script lang="ts">
  import { goto } from 'elegua';
  import { onMount } from 'svelte';
  onMount(() => {
    goto('/new_path');
  });
</script>

File system dynamic routes, like Sveltekit?

I would have implemented this better, but Vite only allows string literals in import.meta.glob() calls, so I end up impolthis had to be manual.

await Promise.all(
  // '/src/posts' is fixed below because vite only accepts literals.
  // If posts dir gets moved, it has to be updated accordingly
  Object.entries(import.meta.glob('/src/posts/**/*.md')).map(async ([path, resolver]) => {
    // ... handle path/resolver, vite style
  })
);

There is an example of this on the demo page.

How to change url but not really triggering page changes and all these store updates?

Just use history.replaceState():

history.replaceState({}, '', '/blog');

If I change the url manually in the browser, will all these stores get updated accordingly?

Of course. That's the point about this lib.

Async routing?

Same as usual. Ex: loading post by hash (async):

http://localhost/blog/#mypost

<script lang="ts">
  import { path, hash } from 'elegua';
</script>

{#if $path === '/blog'}
  {#await loadPost($hash)}
    <p>Loading post {$hash}...</p>
  {:then post}
    <Post data={post} />
  {/await}
{/if}

Can I do partial path matching?

Sure:

{#if $path.startsWith("/blog")}
  <!-- Only pages starting with "/blog" from now on: /blog, /blog/post1, /blog/post2... -->
{/if}

{#if $path.test(/myregexp/)}
  <!-- Match $path against regexp -->
{/if}

Native browser routing

If you want, you can let the browser route the <a> links natively, skipping Elegua. Just add the data-native-router attribute to attribute to the <a> link:

<a href="/blog" data-native-router>Blog</a>

When you can click such links, you can see the browser's "refresh" animation active, indicating the link was loaded from server, skipping Elegua.

I'm getting 404 errors when refreshing urls pointing to paths

Your server must redirect all requests to /index.html so that Elegua gets loaded and handle the routing by itself; otherwise, the server will try to route and you'll probably not get what you were hoping for. For instance, if you load /blog without setting up the server to load /index.html on all requests, it will reply with a 404 error.

In netlify, where the demo is hosted, this is done by adding a _redirect file with the following contents:

/* /index.html 200

Can I use this in Sveltekit?

Yes - see here.

Upgrading from 1.0

Version 1.x used a <Route> component; this version routes using resolve() and $path, which is much cleaner and more flexible.

Benchmarks

No, I'm not benchmarking a client router. However if you care to see the source code, you'll see it's very fast.

Why is this called "Elegua"?

That is the Yoruba deity of the paths, directions, and crossroads. Elegua controls the routes.

License

MIT