Vue open a component in a component - vue.js

Question

In App.vue I have a button to open a component . Inside the component BigForm, I also have a button to open a component named, . But as I open the component. Vue re-render the page with the warning:
The "data" option should be a function that returns a per-instance value in component definitions.
App.Vue
<template>
<div id="app">
<button #click="showModal()">Show</button>
<BigForm v-if="modal" />
</div>
</template>
<script>
import BigForm from "./components/BigForm";
export default {
name: "App",
components: {
BigForm,
},
data() {
return {
modal: false,
};
},
methods: {
showModal() {
this.modal = !this.modal;
},
},
};
</script>
BigForm.vue:
<template>
<div class="hello">
<form style="height: 300px; width: 300px; background-color: green">
<button #click="showSmallForm()">Show small form</button>
<SmallForm
v-if="toggleSmallForm"
style="width: 100px; height: 100px; background-color: yellow"
/>
</form>
</div>
</template>
<script>
import SmallForm from "./SmallForm";
export default {
name: "HelloWorld",
components: {
SmallForm,
},
data() {
return {
toggleSmallForm: false,
};
},
methods: {
showSmallForm() {
this.toggleSmallForm = !this.toggleSmallForm;
},
},
};
</script>
And SmallForm.vue:
<template>
<form>
<input placeholder="Small form input" />
<button>This is small form</button>
</form>
</template>
This is the code to my example in codesandbox:
https://codesandbox.io/s/late-cdn-ssu7f?file=/src/App.vue

Answer 1

The problem is not related to Vue itself but the HTML.
When you use <button> inside <form>, the default type of the button is submit (check this) - when you click the button, the form is submitted to the server causing the page to reload.
You can prevent that by explicitly setting type <button type="button"> (HTML way) or by preventing default action (Vue way) <button #click.prevent="showSmallForm()">Show small form</button> (see event modifiers)
Also note that using <form> in another <form> is not allowed in HTML