svelte:component for dynamic components - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is svelte:component used for in Svelte?

svelte:component lets you render a component dynamically based on a variable. Instead of hardcoding a component, you can choose which one to show at runtime.

beginner

How do you specify which component svelte:component should render?

You pass the component constructor to the this attribute, like <svelte:component this={MyComponent} />.

beginner

Can you pass props to a component rendered with svelte:component? How?

Yes! You pass props just like normal components, by adding attributes inside <svelte:component />. For example: <svelte:component this={MyComponent} name="Alice" />.

intermediate

What happens if the variable passed to this is null or undefined?

No component is rendered. This is useful to conditionally show components dynamically.

intermediate

Why use svelte:component instead of {#if} blocks for dynamic components?

svelte:component is cleaner and scales better when you have many possible components to render. It avoids long {#if} chains and keeps code simple.

How do you tell svelte:component which component to render?

A By wrapping the component inside <code>svelte:component</code> tags

B By importing the component inside <code>svelte:component</code>

C By setting the <code>this</code> attribute to the component variable

D By using <code>bind:this</code> on the component

You specify the component to render dynamically by setting the this attribute to the component variable.

What will happen if this is null in <svelte:component this={null} />?

A No component is rendered

B A default component is rendered

C An error is thrown

D The last rendered component stays visible

If this is null, no component is rendered at all.

Can you pass props to a component rendered with svelte:component?

A No, props are not supported

B Yes, by adding attributes inside <code>&lt;svelte:component /&gt;</code>

C Only if the component is imported dynamically

D Only if you use <code>bind:this</code>

You pass props by adding attributes inside the <svelte:component /> tag, just like normal components.

Which of these is a benefit of using svelte:component?

A It allows rendering components dynamically based on variables

B It automatically optimizes component size

C It replaces the need for <code>{#if}</code> blocks completely

D It compiles components to vanilla JavaScript

svelte:component lets you render components dynamically based on variables.

If you have many possible components to render dynamically, what is the best approach?

A Use <code>bind:this</code> on each component

B Use many nested <code>{#if}</code> blocks

C Render all components and hide them with CSS

D Use <code>svelte:component</code> with a variable holding the component

Using svelte:component with a variable is cleaner and easier to maintain than many {#if} blocks.

Explain how svelte:component helps in rendering components dynamically. Include how to pass props and handle cases when no component should render.

Think about choosing components like picking clothes based on weather.

Describe a scenario where using svelte:component is better than multiple {#if} blocks for showing components.

Imagine a menu with many dishes instead of just two options.

Practice

1. What does the svelte:component tag do in Svelte?

easy

A. It imports components from external libraries.

B. It creates a new Svelte component file.

C. It renders a component dynamically based on a variable.

D. It styles components with CSS.

Solution

1. Step 1: Understand the purpose of svelte:component

   This tag is used to render different components dynamically depending on a variable's value.

2. Step 2: Compare with other options

   Creating files, styling, or importing are unrelated to svelte:component.

3. Final Answer:

   It renders a component dynamically based on a variable. -> Option C

4. Quick Check:

   svelte:component = dynamic rendering [OK]

Hint: Remember: svelte:component means dynamic component rendering [OK]

Common Mistakes:

• Thinking it creates new component files
• Confusing it with CSS styling
• Assuming it imports components

2. Which of the following is the correct syntax to render a dynamic component stored in variable CurrentComp?

easy

A. <component this={CurrentComp} />

B. <svelte:component this={CurrentComp} />

C. <svelte:component src={CurrentComp} />

D. <Component this={CurrentComp} />

Solution

1. Step 1: Recall correct tag and attribute

   The correct tag is svelte:component and the attribute to specify the component is this.

2. Step 2: Check each option

   <svelte:component this={CurrentComp} /> uses correct tag and attribute syntax. Others use wrong tags or attributes.

3. Final Answer:

   <svelte:component this={CurrentComp} /> -> Option B

4. Quick Check:

   Correct tag and this attribute = <svelte:component this={CurrentComp} /> [OK]

Hint: Use svelte:component this={variable} for dynamic components [OK]

Common Mistakes:

• Using component instead of svelte:component
• Using src instead of this
• Capitalizing tags incorrectly

3. Given the code:

  <script>
    import A from './A.svelte';
    import B from './B.svelte';
    let comp = A;
  </script>

  <svelte:component this={comp} />

  <button on:click={() => comp = B}>Switch</button>

What happens when the button is clicked?

medium

A. The displayed component switches from A to B.

B. Nothing changes because comp is not reactive.

C. An error occurs because components cannot be switched dynamically.

D. Both components A and B render at the same time.

Solution

1. Step 1: Understand the initial rendering

   The variable comp starts as component A, so A renders initially.

2. Step 2: Analyze the button click

   Clicking the button sets comp to B, which triggers Svelte to render component B dynamically.

3. Final Answer:

   The displayed component switches from A to B. -> Option A

4. Quick Check:

   Dynamic this changes component = The displayed component switches from A to B. [OK]

Hint: Changing this variable updates the rendered component [OK]

Common Mistakes:

• Thinking dynamic components can't switch
• Assuming comp is not reactive
• Expecting both components to render simultaneously

4. What is wrong with this code snippet?

<script>
  import X from './X.svelte';
  let comp = 'X';
</script>

<svelte:component this={comp} />

medium

A. You cannot use variables inside this.

B. The import statement is incorrect.

C. The svelte:component tag must be self-closing.

D. The variable comp should hold the component, not a string.

Solution

1. Step 1: Check the type of comp

   The variable comp is assigned the string 'X', but it should hold the imported component itself.

2. Step 2: Understand this attribute requirements

   this expects a component reference, not a string name.

3. Final Answer:

   The variable comp should hold the component, not a string. -> Option D

4. Quick Check:

   this needs component, not string [OK]

Hint: Assign component imports, not strings, to this [OK]

Common Mistakes:

• Assigning component name as string
• Thinking svelte:component can't be self-closing
• Believing variables can't be used in this

5. You want to render a dynamic component with props. Given components Cat and Dog both accept a name prop, how do you pass name="Buddy" to the dynamic component stored in petComp?

hard

A. <svelte:component this={petComp} name="Buddy" />

B. <svelte:component this={petComp} {name}="Buddy" />

C. <svelte:component this={petComp} props={{name: 'Buddy'}} />

D. <svelte:component this={petComp} bind:name="Buddy" />

Solution

1. Step 1: Recall how to pass props to components

   Props are passed as attributes directly on the component tag, including svelte:component.

2. Step 2: Check each option's syntax

   <svelte:component this={petComp} name="Buddy" /> correctly passes name="Buddy". <svelte:component this={petComp} {name}="Buddy" /> uses invalid syntax. <svelte:component this={petComp} props={{name: 'Buddy'}} /> tries to pass props as an object, which is not supported. <svelte:component this={petComp} bind:name="Buddy" /> uses bind: incorrectly.

3. Final Answer:

   <svelte:component this={petComp} name="Buddy" /> -> Option A

4. Quick Check:

   Pass props as attributes on svelte:component [OK]

Hint: Pass props like normal attributes on svelte:component [OK]

Common Mistakes:

• Trying to pass props as an object
• Using bind: incorrectly
• Using curly braces around prop name with value