Creating custom directives in Vue - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to register a simple custom directive named 'focus' that sets focus on the element.

Vue

app.directive('focus', {
  mounted(el) {
    el.[1]()
  }
})

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

Ablur

Bclick

Cfocus

Dselect

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'click' instead of 'focus' method.

Forgetting to call the method with parentheses.

Using 'blur' which removes focus instead of setting it.

The focus method sets the keyboard focus on the element.

2fill in blank

medium

Complete the code to define a custom directive that changes the element's background color to the value passed.

Vue

app.directive('bg-color', {
  mounted(el, binding) {
    el.style.backgroundColor = [1]
  }
})

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

Abinding.value

Bbinding.arg

Cbinding.instance

Dbinding.modifiers

Attempts:

3 left

💡 Hint

Common Mistakes

Using binding.arg which is for argument names, not values.

Using binding.modifiers which is an object of flags.

Using binding.instance which refers to the component instance.

The binding.value holds the value passed to the directive, used here to set the background color.

3fill in blank

hard

Fix the error in the directive that tries to log the element's tag name when mounted.

Vue

app.directive('log-tag', {
  mounted(el) {
    console.log(el.[1])
  }
})

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

Atagname

BtagName

Ctag_name

Dtagname()

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase 'tagname' which is undefined.

Trying to call 'tagname()' as a function.

Using underscores which are not valid here.

The correct property to get the tag name is tagName with capital N.

4fill in blank

hard

Fill both blanks to create a directive that updates the element's text content when the bound value changes.

Vue

app.directive('text-update', {
  mounted(el, binding) {
    el.textContent = [1]
  },
  updated(el, binding) {
    el.textContent = [2]
  }
})

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

Abinding.value

Bbinding.oldValue

Cbinding.arg

Dbinding.modifiers

Attempts:

3 left

💡 Hint

Common Mistakes

Using binding.oldValue which is the previous value, not the current.

Using binding.arg or binding.modifiers which are unrelated.

Both mounted and updated hooks should set el.textContent to binding.value to reflect the current value.

5fill in blank

hard

Fill all three blanks to create a directive that adds an event listener on mount, removes it on unmount, and uses the handler passed as the value.

Vue

app.directive('on-click', {
  mounted(el, binding) {
    el.addEventListener('click', [1])
  },
  unmounted(el, binding) {
    el.removeEventListener('click', [2])
  },
  updated(el, binding) {
    el.removeEventListener('click', [3])
    el.addEventListener('click', binding.value)
  }
})

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

Abinding.value

Bbinding.oldValue

Dbinding.arg

Attempts:

3 left

💡 Hint

Common Mistakes

Using binding.arg which is not a function.

Removing the current handler instead of the old one on update.

Not removing the event listener on unmount.

The directive uses binding.value as the current handler and binding.oldValue to remove the previous handler when updated or unmounted.

Practice

1. What is the main purpose of creating a custom directive in Vue?

easy

A. To add reusable behavior to HTML elements

B. To define new components

C. To manage Vuex state

D. To handle routing between pages

Solution

1. Step 1: Understand what directives do in Vue

   Directives are special markers on elements that tell Vue to do something with that element.

2. Step 2: Identify the role of custom directives

   Custom directives let you add reusable behavior to elements, like focusing an input or changing styles dynamically.

3. Final Answer:

   To add reusable behavior to HTML elements -> Option A

4. Quick Check:

   Custom directives = reusable element behavior [OK]

Hint: Custom directives add behavior to elements, not components [OK]

Common Mistakes:

• Confusing directives with components
• Thinking directives manage app state
• Assuming directives handle routing

2. Which of the following is the correct syntax to register a global custom directive named v-focus in Vue 3?

easy

A. Vue.directive('v-focus', function(el) { el.focus() })

B. app.directive('focus', { mounted(el) { el.focus() } })

C. app.directive('v-focus', { bind(el) { el.focus() } })

D. Vue.createDirective('focus', { mounted(el) { el.focus() } })

Solution

1. Step 1: Recall Vue 3 global directive registration

   In Vue 3, you use the app instance's directive method with the directive name without the 'v-' prefix.

2. Step 2: Check the lifecycle hook and syntax

   The correct hook for when the element is inserted is 'mounted', and the function receives the element as argument.

3. Final Answer:

   app.directive('focus', { mounted(el) { el.focus() } }) -> Option B

4. Quick Check:

   Vue 3 global directive = app.directive('name', { mounted }) [OK]

Hint: Use app.directive('name', { mounted }) without 'v-' prefix [OK]

Common Mistakes:

• Including 'v-' prefix in directive name
• Using Vue.directive instead of app.directive in Vue 3
• Using deprecated hooks like 'bind'

3. Given this custom directive registered globally in Vue 3:

app.directive('color', {
  mounted(el, binding) {
    el.style.color = binding.value
  },
  updated(el, binding) {
    el.style.color = binding.value
  }
})

What will be the text color of the paragraph after the component updates if used as <p v-color="'red'">Hello</p> and later the binding value changes to 'blue'?

medium

A. The text color will be black (default)

B. The text color will remain red

C. The text color will change to blue

D. There will be a runtime error

Solution

1. Step 1: Understand directive lifecycle hooks

   The 'mounted' hook sets the color initially, and the 'updated' hook runs when the binding value changes.

2. Step 2: Trace the color change on update

   When the binding value changes to 'blue', the 'updated' hook sets the element's color style to 'blue'.

3. Final Answer:

   The text color will change to blue -> Option C

4. Quick Check:

   updated hook changes color to new binding value [OK]

Hint: updated hook runs on binding change to update element [OK]

Common Mistakes:

• Assuming color stays as initial value
• Ignoring the updated lifecycle hook
• Thinking directive causes errors on update

4. Consider this custom directive code snippet in Vue 3:

app.directive('tooltip', {
  mounted(el, binding) {
    el.setAttribute('title', binding.value)
  },
  updated(el, binding) {
    el.setAttribute('title', binding.oldValue)
  }
})

What is the problem with this directive when the binding value changes?

medium

A. The tooltip title does not update to the new value

B. The directive causes a syntax error

C. The title attribute is removed on update

D. The directive works correctly with no issues

Solution

1. Step 1: Analyze the updated hook usage

   The updated hook sets the title attribute to binding.oldValue, which is the previous value, not the new one.

2. Step 2: Understand the effect on the tooltip

   Because it sets the old value on update, the tooltip does not reflect the new binding value after change.

3. Final Answer:

   The tooltip title does not update to the new value -> Option A

4. Quick Check:

   updated hook must use binding.value, not binding.oldValue [OK]

Hint: Use binding.value in updated hook, not binding.oldValue [OK]

Common Mistakes:

• Using binding.oldValue instead of binding.value on update
• Assuming no update needed for title
• Confusing syntax error with logic error

5. You want to create a custom directive v-auto-focus that automatically focuses an input element only when it is inserted into the DOM and not on updates. Which is the best way to implement this directive in Vue 3?

hard

A. Use the created hook to call el.focus()

B. Use the updated hook to call el.focus() every time the binding changes

C. Use both mounted and updated hooks to call el.focus()

D. Use the mounted hook to call el.focus() and leave updated empty

Solution

1. Step 1: Identify when to focus the element

   The input should be focused only once when inserted, so the 'mounted' hook is the right place.

2. Step 2: Avoid focusing on updates

   Calling focus in 'updated' would focus repeatedly, which is not desired.

3. Step 3: Understand Vue 3 lifecycle hooks

   There is no 'created' hook for directives; 'mounted' is the earliest for DOM access.

4. Final Answer:

   Use the mounted hook to call el.focus() and leave updated empty -> Option D

5. Quick Check:

   Focus on mounted only, not updated [OK]

Hint: Focus in mounted hook only to avoid repeated focusing [OK]

Common Mistakes:

• Focusing in updated hook causing repeated focus
• Using non-existent created hook for directives
• Calling focus multiple times unnecessarily