Home - News ( United States | United Kingdom | Italy | Germany ) - Football scores

Showing content from https://svelte.dev/docs/svelte/$inspect below:

$inspect • Docs • Svelte

$inspect only works during development. In a production build it becomes a noop.

The $inspect rune is roughly equivalent to console.log, with the exception that it will re-run whenever its argument changes. $inspect tracks reactive state deeply, meaning that updating something inside an object or array using fine-grained reactivity will cause it to re-fire (demo):

<script>
	let count = $state(0);
	let message = $state('hello');

	$inspect(count, message); // will console.log when `count` or `message` change
</script>

<button onclick={() => count++}>Increment</button>
<input bind:value={message} />

$inspect returns a property with, which you can invoke with a callback, which will then be invoked instead of console.log. The first argument to the callback is either "init" or "update"; subsequent arguments are the values passed to $inspect (demo):

<script>
	let count = $state(0);

	$inspect(count).with((type, count) => {
		if (type === 'update') {
			debugger; // or `console.trace`, or whatever you want
		}
	});
</script>

<button onclick={() => count++}>Increment</button>

A convenient way to find the origin of some change is to pass console.trace to with:

$inspect(stuff).with(console.trace);

This rune, added in 5.14, causes the surrounding function to be traced in development. Any time the function re-runs as part of an effect or a derived, information will be printed to the console about which pieces of reactive state caused the effect to fire.

<script>
	import { doSomeWork } from './elsewhere';

	$effect(() => {
		// $inspect.trace must be the first statement of a function body
		$inspect.trace();
		doSomeWork();
	});
</script>

$inspect.trace takes an optional first argument which will be used as the label.

RetroSearch is an open source project built by @garambo | Open a GitHub Issue

Search and Browse the WWW like it's 1997 | Search results from DuckDuckGo

HTML: 3.2 | Encoding: UTF-8 | Version: 0.7.4