Directive with arguments and modifiers in Vue - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to bind a click event using a directive with an argument.

Vue

<button v-on:[1]="handleClick">Click me</button>

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

Aclick

Bshow

Cbind

Dmodel

Attempts:

3 left

💡 Hint

Common Mistakes

Using v-bind instead of v-on for events

Omitting the event name argument

The v-on directive listens to DOM events. The argument click specifies the event type.

2fill in blank

medium

Complete the code to use a modifier that prevents the default action on a click event.

Vue

<a href="#" v-on:click.[1]="submitForm">Submit</a>

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

Aprevent

Bstop

Ccapture

Donce

Attempts:

3 left

💡 Hint

Common Mistakes

Using .stop which stops event propagation but not default action

Forgetting the dot before the modifier

The .prevent modifier stops the default browser action, like following a link.

3fill in blank

hard

Fix the error in the directive by correctly adding a modifier to listen only once.

Vue

<button v-on:click[1]="doSomething">Click once</button>

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

A.stop

B.prevent

C.once

D.capture

Attempts:

3 left

💡 Hint

Common Mistakes

Using .prevent or .stop instead of .once

Missing the dot before the modifier

The .once modifier ensures the event handler runs only one time.

4fill in blank

hard

Fill both blanks to bind an input event with modifiers to trim and lazy update.

Vue

<input v-on:input[1][2]="updateValue">

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

A.trim

B.lazy

C.prevent

D.once

Attempts:

3 left

💡 Hint

Common Mistakes

Using .prevent which stops default action unnecessarily

Mixing order of modifiers incorrectly

The .trim modifier removes whitespace, and .lazy updates the model only on change.

5fill in blank

hard

Fill all three blanks to bind a keydown event with argument and modifiers for ctrl key and once.

Vue

<input v-on:keydown[1].[2][3]="handleKey">

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

A.enter

Bctrl

Conce

Dshift

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing argument and modifier syntax

Using .shift instead of .ctrl when Ctrl key is needed

The argument .enter listens for Enter key, .ctrl requires Ctrl key pressed, and .once runs handler once.

Practice

1. In Vue, what does a directive argument specify?
v-bind:title uses title as an argument. What does it do?

easy

A. It adds a CSS class to the element.

B. It changes the directive into a different directive.

C. It tells the directive which attribute or property to target.

D. It defines a new event listener.

Solution

1. Step 1: Understand directive arguments

   Directive arguments specify what part of the element the directive should affect, like an attribute or property.

2. Step 2: Analyze v-bind:title

   Here, title is the argument telling v-bind to bind the value to the element's title attribute.

3. Final Answer:

   It tells the directive which attribute or property to target. -> Option C

4. Quick Check:

   Directive argument = target attribute/property [OK]

Hint: Arguments specify target attribute/property in directives [OK]

Common Mistakes:

• Thinking arguments change directive type
• Confusing arguments with modifiers
• Assuming arguments add CSS classes

2. Which of the following is the correct syntax to use a modifier with a directive argument in Vue?
v-on:click.prevent is an example. Which is correct?

easy

A. v-on:click.prevent

B. v-on.prevent:click

C. v-on:prevent.click

D. v-on:click.prevent()

Solution

1. Step 1: Recall Vue directive syntax

   In Vue, modifiers come after the argument, separated by dots, e.g., v-on:click.prevent.

2. Step 2: Check each option

   v-on:click.prevent matches the correct pattern: directive, colon, argument, dot, modifier. Others mix order or add parentheses incorrectly.

3. Final Answer:

   v-on:click.prevent -> Option A

4. Quick Check:

   Modifiers follow arguments with dots [OK]

Hint: Modifiers come after arguments, separated by dots [OK]

Common Mistakes:

• Placing modifiers before arguments
• Using parentheses with modifiers
• Switching order of argument and modifier

3. What will be the effect of this Vue directive?

<button v-on:click.once.prevent="submit">Submit</button>

medium

A. The submit method runs every click and does not prevent default event.

B. The submit method runs every click and prevents default event.

C. The submit method runs once but does not prevent default event.

D. The submit method runs once on click and prevents default event.

Solution

1. Step 1: Understand modifiers .once and .prevent

   .once makes the event handler run only once. .prevent calls event.preventDefault() to stop default browser behavior.

2. Step 2: Analyze the directive behavior

   The button's click triggers submit only once and prevents default action each time.

3. Final Answer:

   The submit method runs once on click and prevents default event. -> Option D

4. Quick Check:

   .once + .prevent = run once + prevent default [OK]

Hint: Modifiers chain to combine behaviors like once and prevent [OK]

Common Mistakes:

• Ignoring the effect of .once modifier
• Confusing .prevent with .stop
• Assuming method runs multiple times

4. Identify the error in this Vue directive usage:

<input v-model.trim.lazy="username">

medium

A. The directive should be v-model:trim.lazy with an argument.

B. The syntax is correct; no error present.

C. Modifiers .trim and .lazy cannot be used together on v-model.

D. Modifiers must be separated by commas, like .trim,.lazy.

Solution

1. Step 1: Check Vue documentation for v-model modifiers

   Vue allows chaining modifiers like .trim and .lazy on v-model to trim input and update on change.

2. Step 2: Validate syntax correctness

   The syntax v-model.trim.lazy is valid and commonly used. No argument is needed here.

3. Final Answer:

   The syntax is correct; no error present. -> Option B

4. Quick Check:

   Multiple modifiers can chain on v-model [OK]

Hint: Modifiers chain with dots, no commas needed [OK]

Common Mistakes:

• Thinking modifiers need commas
• Assuming arguments are required for modifiers
• Believing some modifiers can't combine

5. You want to create a custom directive v-focus that focuses an input only once when inserted, and you want to pass an argument to specify the delay in milliseconds. Which is the correct way to use arguments and modifiers to achieve this?

<input v-focus:delay.once="500">

hard

A. Use argument delay for delay and modifier .once to focus once.

B. Use modifier .delay for delay and argument once to focus once.

C. Arguments and modifiers cannot be combined in custom directives.

D. Use v-focus.once:delay="500" to apply once and delay.

Solution

1. Step 1: Understand argument and modifier roles

   Arguments specify extra data like 'delay' to the directive. Modifiers like .once change behavior, here to run focus only once.

2. Step 2: Analyze the directive usage

   v-focus:delay.once="500" correctly uses 'delay' as argument and '.once' as modifier. The value '500' is passed as delay time.

3. Final Answer:

   Use argument delay for delay and modifier .once to focus once. -> Option A

4. Quick Check:

   Argument = data, modifier = behavior change [OK]

Hint: Arguments pass data, modifiers change behavior [OK]

Common Mistakes:

• Swapping argument and modifier positions
• Thinking they can't be combined
• Using modifiers as arguments