Component bindings in Svelte - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to bind the input value to the variable.

Svelte

<script>
  let name = '';
</script>

<input type="text" [1]={name}>
<p>Hello, {name}!</p>

Drag options to blanks, or click blank then click option'

Abind:model

Bbind:input

Cbind:text

Dbind:value

Attempts:

3 left

💡 Hint

Common Mistakes

Using bind:input instead of bind:value

Trying to use bind:model which is not valid in Svelte

Forgetting to use bind: prefix

In Svelte, bind:value binds the input's value to the variable, keeping them in sync.

2fill in blank

medium

Complete the code to bind the checkbox checked state to the variable.

Svelte

<script>
  let accepted = false;
</script>

<label>
  <input type="checkbox" [1]={accepted}>
  Accept terms
</label>

Drag options to blanks, or click blank then click option'

Abind:selected

Bbind:value

Cbind:checked

Dbind:state

Attempts:

3 left

💡 Hint

Common Mistakes

Using bind:value which works for text inputs but not checkboxes

Using bind:selected which is for select elements

Using bind:state which is not a valid binding

Checkboxes use bind:checked to bind their checked state to a variable in Svelte.

3fill in blank

hard

Fix the error in binding a select element's value to the variable.

Svelte

<script>
  let color = 'red';
</script>

<select [1]={color}>
  <option value="red">Red</option>
  <option value="green">Green</option>
  <option value="blue">Blue</option>
</select>

Drag options to blanks, or click blank then click option'

Abind:selected

Bbind:value

Cbind:checked

Dbind:option

Attempts:

3 left

💡 Hint

Common Mistakes

Using bind:selected which is not a valid Svelte binding

Using bind:checked which is for checkboxes

Using bind:option which does not exist

For select elements, bind:value binds the selected option's value to the variable.

4fill in blank

hard

Fill both blanks to bind a custom component's prop and listen to its event.

Svelte

<script>
  import Child from './Child.svelte';
  let count = 0;
</script>

<Child [1]={count} on:[2]={() => count++} />

Drag options to blanks, or click blank then click option'

Abind:value

Bclick

Cbind:count

Dchange

Attempts:

3 left

💡 Hint

Common Mistakes

Using bind:value instead of bind:count for the prop

Listening to wrong event name like change instead of click

To bind a prop named count in a child component, use bind:count. To listen for a click event, use on:click.

5fill in blank

hard

Fill all three blanks to bind a textarea value, handle input event, and update a variable.

Svelte

<script>
  let message = '';
  function handleInput(event) {
    [1] = event.target.[2];
  }
</script>

<textarea [3]={message} on:input={handleInput}></textarea>
<p>Message length: {message.length}</p>

Drag options to blanks, or click blank then click option'

Amessage

Bvalue

Cbind:value

Dbind:input

Attempts:

3 left

💡 Hint

Common Mistakes

Using bind:input which is not a valid binding

Trying to update event.target.input instead of event.target.value

Not binding the textarea value

The variable message is updated with the textarea's value. The textarea binds its value with bind:value.

Practice

1. What does bind:value do in a Svelte component?

easy

A. It creates a two-way connection between a variable and an input's value.

B. It only sets the initial value of the input without updating.

C. It listens for clicks on the input element.

D. It disables the input field.

Solution

1. Step 1: Understand bind:value usage

   In Svelte, bind:value links a variable to an input's value so changes update both ways.

2. Step 2: Compare options with behavior

   Only It creates a two-way connection between a variable and an input's value. describes this two-way syncing correctly; others describe unrelated behaviors.

3. Final Answer:

   It creates a two-way connection between a variable and an input's value. -> Option A

4. Quick Check:

   Two-way binding = It creates a two-way connection between a variable and an input's value. [OK]

Hint: Remember: bind:value syncs input and variable both ways [OK]

Common Mistakes:

• Thinking bind:value only sets initial value
• Confusing bind:value with event listeners
• Assuming bind:value disables input

2. Which of the following is the correct syntax to bind a parent's variable count to a child's prop value in Svelte?

easy

A.

B. count

C.

D.

Solution

1. Step 1: Recall Svelte binding syntax

   To bind a parent's variable to a child's prop, use bind:prop={variable} syntax.

2. Step 2: Evaluate options

   <Child bind:value={count} /> matches correct syntax. <Child value={count} /> passes value one-way. Options B and D have invalid syntax.

3. Final Answer:

   <Child bind:value={count} /> -> Option D

4. Quick Check:

   Correct bind syntax = <Child bind:value={count} /> [OK]

Hint: Use bind:prop={variable} to sync parent and child [OK]

Common Mistakes:

• Using curly braces without bind:
• Trying to bind without ={}
• Passing value as child content instead of prop

3. Given this Svelte code:

<script>
  let name = 'Alice';
</script>

<Child bind:name />

<!-- Child.svelte -->
<script>
  export let name;
</script>

<input bind:value={name} />

What happens when the user types 'Bob' in the input?

medium

A. An error occurs because bind:name is invalid.

B. Only the child's name updates; parent stays 'Alice'.

C. The parent's name variable updates to 'Bob' automatically.

D. The input value resets to 'Alice' immediately.

Solution

1. Step 1: Understand two-way binding between parent and child

   The parent binds name to child's name prop with bind:name, syncing both variables.

2. Step 2: Input binding updates child's name and propagates to parent

   Typing in input updates child's name, which updates parent's name automatically.

3. Final Answer:

   The parent's name variable updates to 'Bob' automatically. -> Option C

4. Quick Check:

   Two-way bind updates parent and child = The parent's name variable updates to 'Bob' automatically. [OK]

Hint: bind:prop syncs parent and child variables both ways [OK]

Common Mistakes:

• Thinking only child updates
• Expecting input to reset on typing
• Believing bind:name is invalid syntax

4. Identify the error in this Svelte code snippet:

<script>
  let age = 30;
</script>

<Child bind:age></Child>

<!-- Child.svelte -->
<script>
  export let age;
</script>

<input value={age} />

medium

A. The child input should use bind:value={age} for two-way binding.

B. The parent variable age must be a string, not a number.

C. The child component must not export age to bind it.

D. The parent should use bind:age={age} instead.

Solution

1. Step 1: Check child input binding

   The child input uses value={age}, which is one-way binding only.

2. Step 2: Fix to two-way binding for sync

   To sync changes back to parent, child input must use bind:value={age}.

3. Final Answer:

   The child input should use bind:value={age} for two-way binding. -> Option A

4. Quick Check:

   Two-way input binding needed = The child input should use bind:value={age} for two-way binding. [OK]

Hint: Use bind:value on inputs for two-way sync, not value= alone [OK]

Common Mistakes:

• Using value= instead of bind:value= on inputs
• Thinking export let disables binding
• Misusing bind:age syntax on parent

5. You want to create a custom slider component that updates a parent's volume variable as the slider moves. Which approach correctly uses Svelte component bindings to achieve this?

hard

A. In parent: <Slider value={volume} />In Slider.svelte: export let value; and <input type='range' value={value} />

B. In parent: <Slider bind:value={volume} />In Slider.svelte: export let value; and <input type='range' bind:value={value} />

C. In parent: <Slider bind:volume={volume} />In Slider.svelte: export let volume; and <input type='range' bind:value={volume} />

D. In parent: <Slider bind:value />In Slider.svelte: let value; and <input type='range' bind:value={value} />

Solution

1. Step 1: Understand binding prop names

   The parent binds its volume variable to child's value prop using bind:value={volume}.

2. Step 2: Child exports value and binds input's value to it

   The child exports value and uses bind:value={value} on the input for two-way sync.

3. Step 3: Check other options for errors

   In parent: <Slider value={volume} />
   In Slider.svelte: export let value; and <input type='range' value={value} /> uses one-way binding only. In parent: <Slider bind:volume={volume} />
   In Slider.svelte: export let volume; and <input type='range' bind:value={volume} /> mismatches prop names. In parent: <Slider bind:value />
   In Slider.svelte: let value; and <input type='range' bind:value={value} /> misses binding variable in parent.

4. Final Answer:

   Parent binds volume to child's value; child exports value and binds input value. -> Option B

5. Quick Check:

   Matching bind names and two-way input binding = In parent: <Slider bind:value={volume} />
   In Slider.svelte: export let value; and <input type='range' bind:value={value} /> [OK]

Hint: Bind parent's variable to child's exported prop with same name [OK]

Common Mistakes:

• Mismatching prop names between parent and child
• Using one-way binding instead of bind:value
• Not exporting prop in child component