beforeUpdate and afterUpdate in Svelte - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the beforeUpdate lifecycle function in Svelte?

beforeUpdate runs just before the DOM updates. It lets you run code right before Svelte applies changes to the page.

beginner

When does the afterUpdate lifecycle function run in Svelte?

afterUpdate runs right after the DOM has updated. You can use it to react to changes after the page has changed.

beginner

How do you import <code>beforeUpdate</code> and <code>afterUpdate</code> in a Svelte component?

<p>You import them from <code>svelte</code> like this:<br><code>import { beforeUpdate, afterUpdate } from 'svelte';</code></p>

intermediate

Can beforeUpdate and afterUpdate run multiple times during a component's life?

Yes, they run every time the component updates, not just once. beforeUpdate runs before each update, and afterUpdate runs after each update.

beginner

Give a simple example of using beforeUpdate and afterUpdate in Svelte.

<pre>import { beforeUpdate, afterUpdate } from 'svelte';

let count = 0;

beforeUpdate(() => {
  console.log('About to update the DOM');
});

afterUpdate(() => {
  console.log('DOM updated, count is', count);
});</pre>

When does beforeUpdate run in a Svelte component?

A Only once when the component mounts

B Right after the DOM updates

C Right before the DOM updates

D Only once when the component unmounts

beforeUpdate runs just before the DOM updates each time the component changes.

What is the main use of afterUpdate in Svelte?

A To run code before the DOM updates

B To clean up resources when component unmounts

C To initialize component state

D To run code after the DOM updates

afterUpdate runs after the DOM updates, letting you react to changes on the page.

How often do beforeUpdate and afterUpdate run?

A Only once when the component unmounts

B Every time the component updates

C Only once when the component mounts

D Never, they are deprecated

They run every time the component updates, before and after the DOM changes.

Which import statement is correct to use beforeUpdate and afterUpdate?

A import { beforeUpdate, afterUpdate } from 'svelte';

B import { beforeUpdate, afterUpdate } from 'svelte/internal';

C import beforeUpdate from 'svelte';

D import { beforeUpdate, afterUpdate } from 'react';

You import them directly from svelte like this: import { beforeUpdate, afterUpdate } from 'svelte';

Which lifecycle function would you use to run code right after the DOM changes?

A afterUpdate

B onDestroy

C onMount

D beforeUpdate

afterUpdate runs right after the DOM updates.

Explain the difference between beforeUpdate and afterUpdate in Svelte.

Think about when you want to run code: before or after the page changes.

Describe a simple use case where beforeUpdate and afterUpdate would be helpful in a Svelte component.

Imagine you want to know when the page is about to change and when it has changed.