Special tags

{@html ...}permalink

{@html expression}

In a text expression, characters like < and > are escaped; however, with HTML expressions, they're not.

The expression should be valid standalone HTML — {@html "<div>"}content{@html "</div>"} will not work, because </div> is not valid HTML. It also will not compile Svelte code.

Svelte does not sanitize expressions before injecting HTML. If the data comes from an untrusted source, you must sanitize it, or you are exposing your users to an XSS vulnerability.

<div class="blog-post">
  <h1>{post.title}</h1>
  {@html post.content}
</div>

{@debug ...}permalink

{@debug}

{@debug var1, var2, ..., varN}

The {@debug ...} tag offers an alternative to console.log(...). It logs the values of specific variables whenever they change, and pauses code execution if you have devtools open.

<script>
  let user = {
    firstname: 'Ada',
    lastname: 'Lovelace'
  };
</script>

{@debug user}

<h1>Hello {user.firstname}!</h1>

{@debug ...} accepts a comma-separated list of variable names (not arbitrary expressions).

<!-- Compiles -->
{@debug user}
{@debug user1, user2, user3}

<!-- WON'T compile -->
{@debug user.firstname}
{@debug myArray[0]}
{@debug !isReady}
{@debug typeof user === 'object'}

The {@debug} tag without any arguments will insert a debugger statement that gets triggered when any state changes, as opposed to the specified variables.

{@const ...}permalink

{@const assignment}

The {@const ...} tag defines a local constant.

<script>
  export let boxes;
</script>

{#each boxes as box}
  {@const area = box.width * box.height}
  {box.width} * {box.height} = {area}
{/each}

{@const} is only allowed as direct child of {#if}, {:else if}, {:else}, {#each}, {:then}, {:catch}, <Component /> or <svelte:fragment />.