<template>
  <div>
    <button @click="show = !show">Toggle</button>
    <transition name="fade">
      <p v-if="show">Hello Vue.js!</p>
    </transition>
  </div>
</template>

<script>
export default {
  data() {
    return {
      show: false
    };
  }
};
</script>

<style>
.fade-enter-active, .fade-leave-active {
  transition: opacity 0.5s;
}
.fade-enter, .fade-leave-to {
  opacity: 0;
}
</style>

<template>
  <div>
    <transition name="bounce">
      <button v-if="show" @click="show = false">Click Me!</button>
    </transition>
    <button v-else @click="show = true">Show Button</button>
  </div>
</template>

<script>
export default {
  data() {
    return {
      show: true
    };
  }
};
</script>

<style>
@keyframes bounce {
  0%, 100% {
    transform: translateY(0);
  }
  50% {
    transform: translateY(-20px);
  }
}

.bounce-enter-active {
  animation: bounce 0.5s;
}
</style>

<template>
  <div>
    <button @click="loadData">Load Data</button>
    <div v-if="loading" class="spinner"></div>
    <ul v-else>
      <li v-for="item in items" :key="item.id">{{ item.name }}</li>
    </ul>
  </div>
</template>

<script>
export default {
  data() {
    return {
      loading: false,
      items: []
    };
  },
  methods: {
    async loadData() {
      this.loading = true;
      setTimeout(() => {
        this.items = [
          { id: 1, name: 'Item 1' },
          { id: 2, name: 'Item 2' }
        ];
        this.loading = false;
      }, 2000);
    }
  }
};
</script>

<style>
.spinner {
  width: 40px;
  height: 40px;
  border: 4px solid #ccc;
  border-top: 4px solid #3498db;
  border-radius: 50%;
  animation: spin 1s linear infinite;
}

@keyframes spin {
  0% {
    transform: rotate(0deg);
  }
  100% {
    transform: rotate(360deg);
  }
}
</style>

<template>
  <form @submit.prevent="submitForm">
    <label>
      Name:
      <input v-model="name" />
      <span v-if="nameError" class="error">Name is required</span>
    </label>
    <button type="submit">Submit</button>
  </form>
</template>

<script>
export default {
  data() {
    return {
      name: '',
      nameError: false
    };
  },
  methods: {
    submitForm() {
      if (!this.name) {
        this.nameError = true;
      } else {
        this.nameError = false;
        alert(`Hello, ${this.name}!`);
      }
    }
  }
};
</script>

<style>
.error {
  color: red;
  font-size: 0.8em;
}
</style>

<template>
  <button @click="toggle" :aria-expanded="expanded">
    Toggle Content
  </button>
  <div v-if="expanded">This is the content</div>
</template>

<script>
export default {
  data() {
    return {
      expanded: false
    };
  },
  methods: {
    toggle() {
      this.expanded = !this.expanded;
    }
  }
};
</script>