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Transitions

With Vue.js’ transition system you can apply automatic transition effects when elements are inserted into or removed from the DOM. Vue.js will automatically add/remove CSS classes at appropriate times to trigger CSS transitions or animations for you, and you can also provide JavaScript hook functions to perform custom DOM manipulations during the transition.

To apply transition effects, you need to use the special transition attribute on the target element:

<div v-if="show" transition="my-transition"></div>

The transition attribute can be used together with:

• v-if
• v-show
• v-for (triggered for insertion and removal only)
• Dynamic components (introduced in the next section)
• On a component root node, and triggered via Vue instance DOM methods, e.g. vm.$appendTo(el).

When an element with transition is inserted or removed, Vue will:

1. Try to find a JavaScript transition hooks object registered either through Vue.transition(id, hooks) or passed in with the transitions option, using the id "my-transition". If it finds it, it will call the appropriate hooks at different stages of the transition.

2. Automatically sniff whether the target element has CSS transitions or CSS animations applied, and add/remove the CSS classes at the appropriate times.

3. If no JavaScript hooks are provided and no CSS transitions/animations are detected, the DOM operation (insertion/removal) is executed immediately on next frame.

CSS Transitions

Example

A typical CSS transition looks like this:

<div v-if="show" transition="expand">hello</div>

You also need to define CSS rules for .expand-transition, .expand-enter and .expand-leave classes:

/* always present */
.expand-transition {
  transition: all .3s ease;
  height: 30px;
  padding: 10px;
  background-color: #eee;
  overflow: hidden;
}

/* .expand-enter defines the starting state for entering */
/* .expand-leave defines the ending state for leaving */
.expand-enter, .expand-leave {
  height: 0;
  padding: 0 10px;
  opacity: 0;
}

You can achieve different transitions on the same element by using dynamic binding:

<div v-if="show" :transition="transitionName">hello</div>

new Vue({
  el: '...',
  data: {
    show: false,
    transitionName: 'fade'
  }
})

In addition, you can provide JavaScript hooks:

Vue.transition('expand', {

  beforeEnter: function (el) {
    el.textContent = 'beforeEnter'
  },
  enter: function (el) {
    el.textContent = 'enter'
  },
  afterEnter: function (el) {
    el.textContent = 'afterEnter'
  },
  enterCancelled: function (el) {
    // handle cancellation
  },

  beforeLeave: function (el) {
    el.textContent = 'beforeLeave'
  },
  leave: function (el) {
    el.textContent = 'leave'
  },
  afterLeave: function (el) {
    el.textContent = 'afterLeave'
  },
  leaveCancelled: function (el) {
    // handle cancellation
  }
})

Transition CSS Classes

The classes being added and toggled are based on the value of the transition attribute. In the case of transition="fade", three CSS classes are involved:

1. The class .fade-transition will be always present on the element.

2. .fade-enter defines the starting state of an entering transition. It is applied for a single frame and then immediately removed.

3. .fade-leave defines the ending state of a leaving transition. It is applied when the leaving transition starts and removed when the transition finishes.

If the transition attribute has no value, the classes will default to .v-transition, .v-enter and .v-leave.

Custom Transition Classes

New in 1.0.14

You can specify custom enterClass and leaveClass in the transition definition. These will override the conventional class names. Useful when you want to combine Vue’s transition system with an existing CSS animation library, e.g. Animate.css:

<div v-show="ok" class="animated" transition="bounce">Watch me bounce</div>

Vue.transition('bounce', {
  enterClass: 'bounceInLeft',
  leaveClass: 'bounceOutRight'
})

Declaring Transition Type

New in 1.0.14

Vue.js needs to attach event listeners in order to know when the transition has ended. It can either be transitionend or animationend, depending on the type of CSS rules applied. If you are only using one or the other, Vue.js can automatically detect the correct type. However, if in some cases you want to have both on the same element, for example having a CSS animation triggered by Vue, and also having a CSS transition effect on hover, you will have to explicitly declare the type you want Vue to care about:

Vue.transition('bounce', {
  // Vue will now only care about `animationend` events
  // for this transition
  type: 'animation'
})

Transition Flow Details

When the show property changes, Vue.js will insert or remove the <div> element accordingly, and apply transition classes as specified below:

• When show becomes false, Vue.js will:

  1. Call beforeLeave hook;
  2. Apply v-leave class to the element to trigger the transition;
  3. Call leave hook;
  4. Wait for the transition to finish; (listening to a transitionend event)
  5. Remove the element from the DOM and remove v-leave class;
  6. Call afterLeave hook.

• When show becomes true, Vue.js will:

  1. Call beforeEnter hook;
  2. Apply v-enter class to the element;
  3. Insert it into the DOM;
  4. Call enter hook;
  5. Force a CSS layout so v-enter is actually applied, then remove the v-enter class to trigger a transition back to the element’s original state;
  6. Wait for the transition to finish;
  7. Call afterEnter hook.

In addition, if you remove an element when its enter transition is in progress, the enterCancelled hook will be called to give you the opportunity to clean up changes or timers created in enter. Vice-versa for leaving transitions.

All of the above hook functions are called with their this contexts set to the associated Vue instances. It follows the same rule of compilation scopes: a transition’s this context will point to the scope it is compiled in.

Finally, the enter and leave can optionally take a second callback argument. When you do so, you are indicating that you want to explicitly control when the transition should end, so instead of waiting for the CSS transitionend event, Vue.js will expect you to eventually call the callback to finish the transition. For example:

enter: function (el) {
  // no second argument, transition end
  // determined by CSS transitionend event
}

vs.

enter: function (el, done) {
  // with the second argument, the transition
  // will only end when `done` is called.
}

When multiple elements are being transitioned together, Vue.js batches them and only applies one forced layout.

CSS Animations

CSS animations are applied in the same way with CSS transitions, the difference being that v-enter is not removed immediately after the element is inserted, but on an animationend event.

Example: (omitting prefixed CSS rules here)

<span v-show="show" transition="bounce">Look at me!</span>

.bounce-transition {
  display: inline-block; /* otherwise scale animation won't work */
}
.bounce-enter {
  animation: bounce-in .5s;
}
.bounce-leave {
  animation: bounce-out .5s;
}
@keyframes bounce-in {
  0% {
    transform: scale(0);
  }
  50% {
    transform: scale(1.5);
  }
  100% {
    transform: scale(1);
  }
}
@keyframes bounce-out {
  0% {
    transform: scale(1);
  }
  50% {
    transform: scale(1.5);
  }
  100% {
    transform: scale(0);
  }
}

JavaScript Transitions

You can also use just the JavaScript hooks without defining any CSS rules. When using JavaScript only transitions, the done callbacks are required for the enter and leave hooks, otherwise they will be called synchronously and the transition will finish immediately.

It’s also a good idea to explicitly declare css: false for your JavaScript transitions so that Vue.js can skip the CSS detection. This also prevents cascaded CSS rules from accidentally interfering with the transition.

The following example registers a custom JavaScript transition using jQuery:

Vue.transition('fade', {
  css: false,
  enter: function (el, done) {
    // element is already inserted into the DOM
    // call done when animation finishes.
    $(el)
      .css('opacity', 0)
      .animate({ opacity: 1 }, 1000, done)
  },
  enterCancelled: function (el) {
    $(el).stop()
  },
  leave: function (el, done) {
    // same as enter
    $(el).animate({ opacity: 0 }, 1000, done)
  },
  leaveCancelled: function (el) {
    $(el).stop()
  }
})

Then you can use it with the transition attribute, same deal:

<p transition="fade"></p>

Staggering Transitions

It’s possible to create staggering transitions when using transition with v-for. You can do this either by adding a stagger, enter-stagger or leave-stagger attribute to your transitioned element:

<div v-for="item in list" transition="stagger" stagger="100"></div>

Or, you can provide a stagger, enterStagger or leaveStagger hook for finer-grained control:

Vue.transition('stagger', {
  stagger: function (index) {
    // increase delay by 50ms for each transitioned item,
    // but limit max delay to 300ms
    return Math.min(300, index * 50)
  }
})

Example: