Checkbox and radio bindings in Svelte - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

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

Svelte

<input type="checkbox" bind:checked=[1] />

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

AisChecked

BcheckedValue

Cvalue

Dselected

Attempts:

3 left

💡 Hint

Common Mistakes

Using bind:value instead of bind:checked for checkboxes.

Binding to a variable name not declared in the script.

The bind:checked directive connects the checkbox's checked state to the variable isChecked.

2fill in blank

medium

Complete the code to bind the radio button group to the variable.

Svelte

<input type="radio" name="color" value="red" bind:group=[1] />

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

AselectedColor

BcolorValue

Cchoice

Dcolor

Attempts:

3 left

💡 Hint

Common Mistakes

Using bind:checked instead of bind:group for radio buttons.

Using different variable names for each radio button instead of one group variable.

The bind:group directive binds all radio buttons with the same group to the variable color.

3fill in blank

hard

Fix the error in the checkbox binding code.

Svelte

<input type="checkbox" bind:value=[1] />

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

AisChecked

Bvalue

Cchecked

Dselected

Attempts:

3 left

💡 Hint

Common Mistakes

Using bind:value for checkboxes causes the binding to fail.

Not using any binding directive.

Checkboxes should use bind:checked to bind their checked state, not bind:value.

4fill in blank

hard

Fill both blanks to bind a group of radio buttons and set the variable.

Svelte

<script>
  let [1] = 'blue';
</script>
<input type="radio" name="color" value="blue" bind:group=[2] />

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

AselectedColor

Bcolor

Cchoice

Dselected

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in declaration and binding without matching.

Not initializing the variable with a default value.

The variable selectedColor is declared and bound to the radio group using bind:group={color}. Here, the variable names differ but the binding must match the declared variable.

5fill in blank

hard

Fill all three blanks to create a checkbox bound to a variable and display its state.

Svelte

<script>
  let [1] = false;
</script>
<label>
  <input type="checkbox" bind:checked=[2] />
  Checked: [3]
</label>

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

AisChecked

Bchecked

DcheckedValue

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in declaration, binding, and display.

Binding to bind:value instead of bind:checked.

The variable isChecked is declared and bound to the checkbox's checked state. The label displays the current value of isChecked.

Practice

1. In Svelte, which binding is used to track whether a single checkbox is checked or not?

easy

A. bind:group

B. bind:value

C. bind:checked

D. bind:selected

Solution

1. Step 1: Understand checkbox binding

   Checkboxes in Svelte use bind:checked to track true/false state.

2. Step 2: Differentiate from other bindings

   bind:value is for input values, bind:group is for radio or multiple checkboxes, bind:selected is invalid.

3. Final Answer:

   <code>bind:checked</code> -> Option C

4. Quick Check:

   Checkbox true/false = bind:checked [OK]

Hint: Checkbox true/false uses bind:checked [OK]

Common Mistakes:

• Using bind:value for checkbox state
• Confusing bind:group with bind:checked
• Trying bind:selected which doesn't exist

2. Which of the following is the correct syntax to bind a group of radio buttons to a variable color in Svelte?

easy

A. <input type='radio' bind:checked={color} value='red' />

B. <input type='radio' bind:selected={color} value='red' />

C. <input type='radio' bind:value={color} value='red' />

D. <input type='radio' bind:group={color} value='red' />

Solution

1. Step 1: Identify radio button binding

   Radio buttons use bind:group to bind multiple inputs to one variable.

2. Step 2: Check syntax correctness

   Only bind:group={color} correctly binds the group to variable color.

3. Final Answer:

   <input type='radio' bind:group={color} value='red' /> -> Option D

4. Quick Check:

   Radio group binding = bind:group [OK]

Hint: Radio buttons bind group with bind:group [OK]

Common Mistakes:

• Using bind:checked for radio groups
• Using bind:value instead of bind:group
• Using bind:selected which is invalid

3. Given this Svelte code:

<script>
  let selectedColors = [];
</script>
<input type='checkbox' bind:group={selectedColors} value='red' /> Red
<input type='checkbox' bind:group={selectedColors} value='blue' /> Blue
<input type='checkbox' bind:group={selectedColors} value='green' /> Green

<p>Selected: {JSON.stringify(selectedColors)}</p>

If the user checks 'red' and 'green', what will be displayed inside the paragraph?

medium

A. Selected: ["red", "green"]

B. Selected: ["red"]

C. Selected: [true, true]

D. Selected: red, green

Solution

1. Step 1: Understand bind:group with checkboxes

   Binding multiple checkboxes with bind:group stores selected values in an array.

2. Step 2: Check which values are selected

   User selects 'red' and 'green', so array contains ["red", "green"].

3. Final Answer:

   Selected: ["red", "green"] -> Option A

4. Quick Check:

   Checkbox group array = ["red", "green"] [OK]

Hint: Multiple checkboxes bind:group stores array of values [OK]

Common Mistakes:

• Expecting boolean array instead of values
• Confusing bind:checked with bind:group
• Outputting string instead of JSON array

4. Consider this Svelte snippet:

<script>
  let fruit = 'apple';
</script>
<input type='radio' bind:checked={fruit} value='apple' /> Apple
<input type='radio' bind:group={fruit} value='banana' /> Banana

What is the main issue with this code?

medium

A. Using bind:group with a string variable is invalid

B. Mixing bind:checked and bind:group on radio buttons causes inconsistent binding

C. Missing bind:value on radio inputs

D. Radio buttons must use bind:checked, not bind:group

Solution

1. Step 1: Identify bindings on radio buttons

   One radio uses bind:checked, the other uses bind:group on the same variable.

2. Step 2: Understand correct radio binding

   Radio buttons must all use bind:group to bind to one variable consistently.

3. Final Answer:

   Mixing bind:checked and bind:group on radio buttons causes inconsistent binding -> Option B

4. Quick Check:

   Radio group must use bind:group consistently [OK]

Hint: Use bind:group consistently for all radios in a group [OK]

Common Mistakes:

• Using bind:checked on radios instead of bind:group
• Mixing different bindings on radios
• Assuming bind:value binds radio group

5. You want to create a Svelte form where users can select multiple toppings from checkboxes and also pick a single pizza size with radio buttons. Which of the following code snippets correctly binds the toppings to an array selectedToppings and the size to a string pizzaSize?

hard

A. <script>
let selectedToppings = [];
let pizzaSize = '';
</script>
<input type='checkbox' bind:group={selectedToppings} value='pepperoni' /> Pepperoni
<input type='checkbox' bind:group={selectedToppings} value='mushrooms' /> Mushrooms
<input type='radio' bind:group={pizzaSize} value='small' /> Small
<input type='radio' bind:group={pizzaSize} value='large' /> Large

B. <script>
let selectedToppings = '';
let pizzaSize = [];
</script>
<input type='checkbox' bind:checked={selectedToppings} value='pepperoni' /> Pepperoni
<input type='checkbox' bind:checked={selectedToppings} value='mushrooms' /> Mushrooms
<input type='radio' bind:checked={pizzaSize} value='small' /> Small
<input type='radio' bind:checked={pizzaSize} value='large' /> Large

C. <script>
let selectedToppings = [];
let pizzaSize = '';
</script>
<input type='checkbox' bind:checked={selectedToppings} value='pepperoni' /> Pepperoni
<input type='checkbox' bind:checked={selectedToppings} value='mushrooms' /> Mushrooms
<input type='radio' bind:value={pizzaSize} value='small' /> Small
<input type='radio' bind:value={pizzaSize} value='large' /> Large

D. <script>
let selectedToppings = [];
let pizzaSize = '';
</script>
<input type='checkbox' bind:group={selectedToppings} value='pepperoni' /> Pepperoni
<input type='checkbox' bind:group={selectedToppings} value='mushrooms' /> Mushrooms
<input type='radio' bind:checked={pizzaSize} value='small' /> Small
<input type='radio' bind:checked={pizzaSize} value='large' /> Large

Solution

1. Step 1: Bind multiple checkboxes to an array

   Use bind:group on checkboxes to bind selected values to an array variable.

2. Step 2: Bind radio buttons to a string variable

   Use bind:group on radio buttons to bind the selected value to a string variable.

3. Step 3: Verify correct syntax in options

   <script>
     let selectedToppings = [];
     let pizzaSize = '';
   </script>
   <input type='checkbox' bind:group={selectedToppings} value='pepperoni' /> Pepperoni
   <input type='checkbox' bind:group={selectedToppings} value='mushrooms' /> Mushrooms
   <input type='radio' bind:group={pizzaSize} value='small' /> Small
   <input type='radio' bind:group={pizzaSize} value='large' /> Large

   correctly uses bind:group for both checkboxes and radios with proper variables.

4. Final Answer:

   Option A code snippet -> Option A

5. Quick Check:

   Checkbox array + radio string = bind:group [OK]

Hint: Use bind:group for checkbox arrays and radio groups [OK]

Common Mistakes:

• Using bind:checked for multiple checkboxes array
• Using bind:checked for radio groups
• Mixing bind:value and bind:checked incorrectly