Group bindings in Svelte - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a group binding in Svelte?

A group binding in Svelte lets you link multiple inputs (like radio buttons or checkboxes) to a single variable, so they share the same value or state automatically.

beginner

How do you bind a group of radio buttons to one variable in Svelte?

Use the bind:group directive on each radio button with the same variable name. This way, only one radio button can be selected, and the variable holds the selected value.

intermediate

What happens when you change the bound variable in a group binding?

Changing the bound variable updates which input in the group is selected. The UI and the variable stay in sync automatically.

intermediate

Can group bindings be used with checkboxes in Svelte?

Yes. When binding a group of checkboxes, the bound variable is usually an array that holds all selected values. Checking or unchecking updates the array automatically.

beginner

Why are group bindings helpful in forms?

They simplify managing multiple related inputs by syncing their state with one variable. This reduces code and keeps UI and data consistent.

In Svelte, what does bind:group do when used on radio buttons?

A Disables all radio buttons

B Makes each radio button independent

C Changes the radio buttons to checkboxes

D Links all radios to one variable to track the selected value

bind:group connects radio buttons so only one can be selected and the variable holds that value.

What type of variable do you bind to a group of checkboxes in Svelte?

A An array

B A string

C A number

D A boolean

Checkbox groups bind to an array holding all selected values.

If you update the bound variable of a radio group in Svelte, what happens?

A The UI does not change

B The selected radio button updates to match the variable

C All radio buttons become unchecked

D An error occurs

The UI updates automatically to reflect the variable's value.

Which directive is used to bind a group of inputs in Svelte?

A bind:value

B bind:checked

C bind:group

D bind:this

bind:group is the directive for group bindings.

Why use group bindings instead of individual bindings for each input?

A To write less code and keep inputs in sync

B To disable inputs

C To make inputs invisible

D To prevent user interaction

Group bindings simplify code and keep UI and data consistent.

Explain how group bindings work in Svelte with radio buttons.

Think about how radio buttons share one choice.

Describe how to use group bindings with checkboxes in Svelte and what the bound variable represents.

Checkboxes can have many selections.

Practice

1. In Svelte, what does a group binding do when used with multiple checkboxes?

easy

A. It connects all checkboxes to a single array variable that holds selected values.

B. It links each checkbox to a separate variable automatically.

C. It disables all checkboxes except one.

D. It creates a radio button group instead of checkboxes.

Solution

1. Step 1: Understand group binding with checkboxes

   Group binding in Svelte with checkboxes uses an array variable to store all selected checkbox values.

2. Step 2: Recognize the effect on state

   When a checkbox is checked or unchecked, the array updates automatically to reflect the current selections.

3. Final Answer:

   It connects all checkboxes to a single array variable that holds selected values. -> Option A

4. Quick Check:

   Checkbox group binding = array variable [OK]

Hint: Checkbox groups bind to arrays holding all selected values [OK]

Common Mistakes:

• Thinking each checkbox needs its own variable
• Confusing checkbox groups with radio groups
• Assuming group binding disables inputs

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

easy

A.

B.

C.

D.

Solution

1. Step 1: Recall Svelte group binding syntax

   For radio buttons, Svelte uses bind:group to connect all radios to one variable.

2. Step 2: Match syntax with options

   uses bind:group={selected}, which is the correct syntax for radio groups.

3. Final Answer:

   <input type="radio" bind:group={selected} value="A"> -> Option A

4. Quick Check:

   Radio group binding syntax = bind:group [OK]

Hint: Use bind:group for radio button groups in Svelte [OK]

Common Mistakes:

• Using bind:value instead of bind:group
• Using bind:checked which is for single checkbox
• Incorrect attribute order or spelling

3. Consider this Svelte code snippet:

<script>
  let selectedFruits = [];
</script>

<label><input type="checkbox" bind:group={selectedFruits} value="apple"> Apple</label>
<label><input type="checkbox" bind:group={selectedFruits} value="banana"> Banana</label>
<label><input type="checkbox" bind:group={selectedFruits} value="cherry"> Cherry</label>

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

If the user checks Apple and Cherry, what will be displayed inside the <p> tag?

medium

A. Selected: {apple, cherry}

B. Selected: ["banana"]

C. Selected: apple,cherry

D. Selected: ["apple", "cherry"]

Solution

1. Step 1: Understand checkbox group binding behavior

   When checkboxes are bound to an array, each checked box's value is added to the array.

2. Step 2: Identify selected checkboxes and output format

   User checked Apple and Cherry, so array is ["apple", "cherry"]. JSON.stringify shows this as a JSON array string.

3. Final Answer:

   Selected: ["apple", "cherry"] -> Option D

4. Quick Check:

   Checkbox group array output = JSON array string [OK]

Hint: Checkbox group values appear as array strings in output [OK]

Common Mistakes:

• Expecting a comma-separated string instead of array
• Confusing selected values with unchecked ones
• Misreading JSON.stringify output format

4. This Svelte code tries to bind a group of checkboxes but does not work as expected:

<script>
  let selected = "";
</script>

<input type="checkbox" bind:group={selected} value="x">
<input type="checkbox" bind:group={selected} value="y">

What is the main problem here?

medium

A. The value attribute is missing from the inputs.

B. The variable 'selected' should be an array, not a string, for checkbox group binding.

C. Checkbox inputs cannot use bind:group in Svelte.

D. bind:group only works with radio buttons, not checkboxes.

Solution

1. Step 1: Check variable type for checkbox group binding

   Checkbox group binding requires the bound variable to be an array to hold multiple selected values.

2. Step 2: Identify the error in variable initialization

   The code uses a string variable instead of an array, causing binding to fail or behave incorrectly.

3. Final Answer:

   The variable 'selected' should be an array, not a string, for checkbox group binding. -> Option B

4. Quick Check:

   Checkbox group variable must be array [OK]

Hint: Checkbox group variables must be arrays, not strings [OK]

Common Mistakes:

• Using string instead of array for checkbox group
• Thinking bind:group is only for radios
• Forgetting to set value attribute on inputs

5. You want to create a Svelte form where users select their favorite colors from checkboxes and also pick one preferred shape from radio buttons. Which is the best way to bind these inputs to variables colors and shape respectively?

hard

A. let colors = []; with bind:group={colors} on radios, and let shape = ''; with bind:group={shape} on checkboxes.

B. let colors = ''; with bind:value={colors} on checkboxes, and let shape = []; with bind:group={shape} on radios.

C. let colors = []; with bind:group={colors} on checkboxes, and let shape = ''; with bind:group={shape} on radios.

D. let colors = ''; with bind:group={colors} on checkboxes, and let shape = ''; with bind:value={shape} on radios.

Solution

1. Step 1: Assign correct variable types for inputs

   Checkbox groups bind to arrays to hold multiple selections; radio groups bind to single values (strings).

2. Step 2: Match bindings to input types

   Checkboxes use bind:group with an array variable; radios use bind:group with a string variable.

3. Final Answer:

   let colors = [] with bind:group on checkboxes, let shape = '' with bind:group on radios -> Option C

4. Quick Check:

   Checkboxes = array, radios = string with bind:group [OK]

Hint: Checkbox groups use arrays; radio groups use single values [OK]

Common Mistakes:

• Swapping variable types between checkboxes and radios
• Using bind:value instead of bind:group for groups
• Initializing variables with wrong types