logic relies on once per tick evaluation (courtesy of Rich Harris) • Playground • Svelte

App.svelte

let temperature = 50;

let previous;

let direction = null;

// if this block ran more than once per tick it would always show "cooler"

$: {

if (previous !== undefined) {

direction = temperature > previous

? 'warmer'

: 'cooler';

}

previous = temperature;

}

</script>

{#if direction}

<p>the temperature is getting {direction}</p>

{/if}

import 'svelte/internal/disclose-version';

import 'svelte/internal/flags/legacy';

import * as $ from 'svelte/internal/client';

var root_1 = $.template(`<p> </p>`);

var root = $.template(`<input type="range"> <!>`, 1);

export default function App($$anchor, $$props) {

$.push($$props, false);

let temperature = $.mutable_state(50);

let previous = $.mutable_state();

let direction = $.mutable_state(null);

$.legacy_pre_effect(() => ($.get(previous), $.get(temperature)), () => {

if ($.get(previous) !== undefined) {

$.set(direction, $.get(temperature) > $.get(previous) ? 'warmer' : 'cooler');

}

$.set(previous, $.get(temperature));

});

$.legacy_pre_effect_reset();

var fragment = root();

var input = $.first_child(fragment);

$.remove_input_defaults(input);

var node = $.sibling(input, 2);

{

var consequent = ($$anchor) => {

var p = root_1();

var text = $.child(p);

result = svelte.compile(source, {

generate: "client" "server",

dev: false });

/* Add a <style> tag to see the CSS output */

		
			
				
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 }
 ]
sourceType: "module"
 }
attributes: []
 }
 }

The AST is not public API and may change at any point in time

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