Informs users while preserving the current page state.
### Basic usage
Dialog pops up a dialog box, and it's quite customizable.
:::demo Set the `visible` attribute with a `Boolean`, and Dialog shows when it is `true`. The Dialog has two parts: `body` and `footer`, and the latter requires a `slot` named `footer`. The optional `title` attribute (empty by default) is for defining a title. Finally, this example demonstrates how `before-close` is used.
```html
<el-buttontype="text"@click="dialogVisible =true">click to open the Dialog</el-button>
`before-close` only works when user clicks the close icon or the backdrop. If you have buttons that close the Dialog in the `footer` named slot, you can add what you would do with `before-close` in the buttons' click event handler.
If a Dialog is nested in another Dialog, `append-to-body` is required.
:::demo Normally we do not recommend using nested Dialog. If you need multiple Dialogs rendered on the page, you can simply flat them so that they're siblings to each other. If you must nest a Dialog inside another Dialog, set `append-to-body` of the nested Dialog to true, and it will append to body instead of its parent node, so both Dialogs can be correctly rendered.
```html
<template>
<el-buttontype="text"@click="outerVisible =true">open the outer Dialog</el-button>
:::demo Setting `center` to `true` will center dialog's header and footer horizontally. `center` only affects Dialog's header and footer. The body of Dialog can be anything, so sometimes it may not look good when centered. You need to write some CSS if you wish to center the body as well.
The content of Dialog is lazily rendered, which means the default slot is not rendered onto the DOM until it is firstly opened. Therefore, if you need to perform a DOM manipulation or access a component using `ref`, do it in the `open` event callback.
When this is feature is enabled, the content under default slot will be destroyed with a `v-if` directive. Enable this when you have perf concerns.
:::demo Note that by enabling this feature, the content will not be rendered before `transition.beforeEnter` dispatched, there will only be `overlay``header(if any)``footer(if any)`.
```html
<el-buttontype="text"@click="centerDialogVisible =true">Click to open Dialog</el-button>
<el-dialog
title="Notice"
v-model="centerDialogVisible"
width="30%"
destroy-on-close
center>
<span>Notice: before dialog gets opened for the first time this node and the one bellow will not be rendered</span>
When using `modal` = false, please make sure that `append-to-body` was set to **true**, because `Dialog` was positioned by `position: relative`, when `modal` gets removed, `Dialog` will position itself based on the current position in the DOM, instead of `Document.Body`, thus the style will be messed up.
