Iterate through object in svelte

2 min read 05-10-2024

Looping Through Objects in Svelte: A Comprehensive Guide

Svelte, the reactive JavaScript framework, makes working with data incredibly intuitive. But what happens when your data is stored in an object, and you need to iterate through it? Fear not! This article will guide you through looping through objects in Svelte, empowering you to harness the full power of this versatile framework.

The Challenge: Iterating Through Objects

Imagine you have a Svelte component that displays information about different fruits. This information is conveniently organized in an object:

let fruits = {
  apple: {
    color: "red",
    taste: "sweet"
  },
  banana: {
    color: "yellow",
    taste: "sweet"
  },
  orange: {
    color: "orange",
    taste: "tangy"
  }
};

Now, you want to display each fruit's properties in your component's template. The challenge lies in effectively looping through the fruits object and accessing its key-value pairs.

The Solution: Object.entries

Svelte utilizes the {#each} directive for iterating over data. While {#each} works beautifully with arrays, we need a way to transform our object into an iterable format. Enter Object.entries(), a built-in JavaScript function that takes an object and returns an array of key-value pairs.

Here's how we can use Object.entries() to achieve our desired output:

<script>
  let fruits = {
    apple: {
      color: "red",
      taste: "sweet"
    },
    banana: {
      color: "yellow",
      taste: "sweet"
    },
    orange: {
      color: "orange",
      taste: "tangy"
    }
  };
</script>

<ul>
  {#each Object.entries(fruits) as [fruit, properties]}
    <li>
      <h3>{fruit}</h3>
      <p>Color: {properties.color}</p>
      <p>Taste: {properties.taste}</p>
    </li>
  {/each}
</ul>

This code snippet demonstrates the following:

We use Object.entries(fruits) to obtain an array of [fruit, properties] pairs.
The {#each} directive iterates over this array.
For each pair, fruit holds the key (e.g., "apple"), and properties holds the corresponding object containing the fruit's details.

Key Considerations:

Order of Iteration: Object.entries() doesn't guarantee a specific order of iteration. If you need a consistent order, you can use methods like Object.keys() followed by sorting, or consider using a Map instead of an object.
Destructuring: Destructuring assignment within the {#each} directive (like [fruit, properties]) provides a concise way to extract individual values.
Reactivity: Changes to the fruits object will automatically trigger re-rendering in your Svelte component, ensuring your list updates in real-time.

Practical Example: Dynamically Changing Properties

Let's imagine you want to dynamically update the taste of a fruit based on user interaction. We can use Object.entries() and a for...in loop to easily modify the properties:

<script>
  let fruits = {
    apple: {
      color: "red",
      taste: "sweet"
    },
    banana: {
      color: "yellow",
      taste: "sweet"
    },
    orange: {
      color: "orange",
      taste: "tangy"
    }
  };

  function updateTaste(fruit, newTaste) {
    for (const key in fruits) {
      if (key === fruit) {
        fruits[key].taste = newTaste;
      }
    }
  }
</script>

<ul>
  {#each Object.entries(fruits) as [fruit, properties]}
    <li>
      <h3>{fruit}</h3>
      <p>Color: {properties.color}</p>
      <p>Taste: {properties.taste}</p>
      <button on:click={() => updateTaste(fruit, 'sour')}>Make Sour</button>
    </li>
  {/each}
</ul>

This code allows the user to change the taste of any fruit by clicking the "Make Sour" button. The updateTaste function dynamically updates the fruits object, which triggers a re-render and updates the UI accordingly.

Conclusion:

Looping through objects in Svelte is straightforward and powerful. By leveraging the Object.entries() function alongside the {#each} directive, you can easily access, modify, and display data stored in objects within your Svelte components. Remember to consider reactivity and order of iteration as you implement these techniques for optimal and intuitive user experiences.