What is await block in Svelte?
Svelte, unlike traditional frameworks such as React, Angular, or Vue, functions as a compiler with remarkable versatility known for its innovative approach to reactive web development. It distinguishes itself by not relying on a virtual DOM; instead, it compiles directly to vanilla JavaScript and interacts with the DOM. This unique approach results in highly efficient JavaScript output, which is notably compact compared to its counterparts, and consequently, it delivers impressive performance. Among its features, the await block stands out as a powerful tool for handling asynchronous operations.
The await block in Svelte is designed to simplify asynchronous programming. It allows us to await promises and handle the asynchronous resolution seamlessly, resulting in cleaner and more maintainable code. This block is particularly useful when dealing with tasks like data fetching from APIs or database calls, where response times can vary.
Syntax of the await block
To use the await block in Svelte, we typically define it within our component’s script section. Here’s a simplified syntax:
<script>let data;const fetchData = async () => {const response = await fetch('https://api.example.com/data');data = await response.json();};</script><main><await promise={fetchData()}>{#then data}<!-- Render the data when the promise resolves --><p>{data}</p>{:then}<!-- Render a loading state or handle errors --><p>Loading...</p>{/then}</await></main>
We define a variable
datato store the fetched data.The
fetchDatafunction is marked asasync, and it makes an asynchronous request to an API.Inside the
awaitblock, the{#then}block is used to render content when the promise resolves successfully, and{:then}is used for handling loading states or errors.
FLowchart
The following diagram illustrates the flow of control of the await block in Svelte:
Fetching data from an API
Let’s consider a scenario where we need to fetch data from a remote API and display it in our Svelte app. The await block simplifies this process:
<script>
let data = null; // Initialize a variable to store fetched data as null
// Define an asynchronous function named 'fetchData'
async function fetchData() {
// Asynchronously fetch data from an API
const response = await fetch('https://jsonplaceholder.typicode.com/todos/1');
// Asynchronously parse the response as JSON
const jsonData = await response.json();
// Store the parsed data in the 'data' variable
data = jsonData;
}
// Call the 'fetchData' function to initiate data fetching
fetchData();
</script>
<main>
<h1>Svelte data fetching example with await block</h1>
<!-- If 'data' is truthy (not null), execute the following statements -->
{#if data}
<ul>
<li>
<!-- Display the 'userId' property from the 'data' -->
<strong>User ID:</strong> {data.userId}
</li>
<li>
<!-- Display the 'id' property from the 'data' -->
<strong>ID:</strong> {data.id}
</li>
<li>
<!-- Display the 'title' property from the 'data' -->
<strong>Title:</strong> {data.title}
</li>
</ul>
<!-- If 'data' is falsy (null), execute the following statements -->
{:else}
<!-- Display a loading message -->
<p>Loading data...</p>
{/if}
</main>Note: Try changing the
https://jsonplaceholder.typicode.com/todos/1" value fromto any other value and observe the change in the output.
Code explanation
Now, let’s break down the code line by line:
Line 2: Initializes a variable
datato store fetched data and set it tonull. This variable will be used to hold the fetched JSON data.Line 5: Defines an asynchronous function
fetchData. Inside this function, we will make an asynchronous API request to fetch data.Line 7: Makes an asynchronous API request using the
fetchfunction to get data from the specified URL (JSONPlaceholder API). We fetch data related to a specific to-do item with an ID of. Line 9: Asynchronously parses the response from the API as JSON and stores it in the
jsonDatavariable.Line 11: Assigns the parsed JSON data stored in the
jsonDatavariable to thedatavariable. This step effectively populates thedatavariable with the fetched data.Line 15: Calls the
fetchDatafunction immediately to start the process of fetching and updating the data.Line 19: Displays a heading in the main content area of the component to provide context for what the component does.
Line 21: Starts a conditional block with
{#if data}. This block checks whether thedatavariable is truthy (notnull).Line 25: Displays the label “User ID” and the actual
userIdproperty from thedatavariable.Line 29: Displays the label “ID” and the
idproperty from thedatavariable.Line 33: Displays the label “Title” and the
titleproperty from thedatavariable.Line 37: In the
{:else}block, handle the case wheredatais falsy (null), indicating that data is still being fetched.Line 40: Displays a loading message indicating that data is in the process of being fetched.
Conclusion
The await block in Svelte simplifies handling asynchronous operations, making our code cleaner and more readable. It’s a powerful tool for fetching and displaying data from external sources in our Svelte applications. By understanding how to use the await block, we can create responsive and efficient web applications that provide a seamless user experience.
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