## MessageBox

A set of modal boxes simulating system message box, mainly for alerting information, confirm operations and prompting messages.
:::tip
By design MessageBox provides simulations of system's `alert`, `confirm` and `prompt`，so it's content should be simple. For more complicated contents, please use Dialog.
:::

### Alert

Alert interrupts user operation until the user confirms.

:::demo Open an alert by calling the `$alert` method. It simulates the system's `alert`, and cannot be closed by pressing ESC or clicking outside the box. In this example, two parameters `message` and `title` are received. It is worth mentioning that when the box is closed, it returns a `Promise` object for further processing. If you are not sure if your target browsers support `Promise`, you should import a third party polyfill or use callbacks instead like this example.

```html
<template>
  <el-button type="text" @click="open">Click to open the Message Box</el-button>
</template>

<script>
  export default {
    methods: {
      open() {
        this.$alert('This is a message', 'Title', {
          confirmButtonText: 'OK',
          callback: action => {
            this.$message({
              type: 'info',
              message: `action: ${ action }`
            });
          }
        });
      }
    }
  }
</script>
```
:::

### Confirm

Confirm is used to ask users' confirmation.

:::demo Call `$confirm` method to open a confirm, and it simulates the system's `confirm`. We can also highly customize Message Box by passing a third attribute `options` which is a literal object. The attribute `type` indicates the message type, and it's value can be `success`, `error`, `info` and `warning`. Note that the second attribute `title` must be a `string`, and if it is an `object`, it will be handled as the attribute `options`. Here we use `Promise` to handle further processing. 

```html
<template>
  <el-button type="text" @click="open">Click to open the Message Box</el-button>
</template>

<script>
  export default {
    methods: {
      open() {
        this.$confirm('This will permanently delete the file. Continue?', 'Warning', {
          confirmButtonText: 'OK',
          cancelButtonText: 'Cancel',
          type: 'warning'
        }).then(() => {
          this.$message({
            type: 'success',
            message: 'Delete completed'
          });
        }).catch(() => {
          this.$message({
            type: 'info',
            message: 'Delete canceled'
          });          
        });
      }
    }
  }
</script>
```

:::

### Prompt

Prompt is used when user input is required.

:::demo Call `$prompt` method to open a prompt, and it simulates the system's `prompt`. You can use `inputPattern` parameter to specify your own RegExp pattern. Use `inputValidator` to specify validation method, and it should return `Boolean` or `String`. Returning `false` or `String` means the validation has failed, and the string returned will be used as the `inputErrorMessage`. In addition, you can customize the placeholder of the input box with `inputPlaceholder` parameter.

```html
<template>
  <el-button type="text" @click="open">Click to open Message Box</el-button>
</template>

<script>
  export default {
    methods: {
      open() {
        this.$prompt('Please input your e-mail', 'Tip', {
          confirmButtonText: 'OK',
          cancelButtonText: 'Cancel',
          inputPattern: /[\w!#$%&'*+/=?^_`{|}~-]+(?:\.[\w!#$%&'*+/=?^_`{|}~-]+)*@(?:[\w](?:[\w-]*[\w])?\.)+[\w](?:[\w-]*[\w])?/,
          inputErrorMessage: 'Invalid Email'
        }).then(({ value }) => {
          this.$message({
            type: 'success',
            message: 'Your email is:' + value
          });
        }).catch(() => {
          this.$message({
            type: 'info',
            message: 'Input canceled'
          });       
        });
      }
    }
  }
</script>
```
:::

### Customization

Can be customized to show various content.

:::demo The three methods mentioned above are repackagings of the `$msgbox` method. This example calls `$msgbox` method directly using the `showCancelButton` attribute, which is used to indicate if a cancel button is displayed. Besides we can use `cancelButtonClass` to add a custom style and `cancelButtonText` to customize the button text (the confirm button also has these fields, and a complete list of fields can be found at the end of this documentation). This example also uses the `beforeClose` attribute. It is a method and will be triggered when the MessageBox instance will be closed, and its execution will stop the instance from closing. It has three parameters: `action`, `instance` and `done`. Using it enables you to manipulate the instance before it closes, e.g. activating `loading` for confirm button; you can invoke the `done` method to close the MessageBox instance (if `done` is not called inside `beforeClose`, the instance will not be closed).

```html
<template>
  <el-button type="text" @click="open">Click to open Message Box</el-button>
</template>

<script>
  export default {
    methods: {
      open() {
        const h = this.$createElement;
        this.$msgbox({
          title: 'Message',
          message: h('p', null, [
            h('span', null, 'Message can be '),
            h('i', { style: 'color: teal' }, 'VNode')
          ]),
          showCancelButton: true,
          confirmButtonText: 'OK',
          cancelButtonText: 'Cancel',
          beforeClose: (action, instance, done) => {
            if (action === 'confirm') {
              instance.confirmButtonLoading = true;
              instance.confirmButtonText = 'Loading...';
              setTimeout(() => {
                done();
                setTimeout(() => {
                  instance.confirmButtonLoading = false;
                }, 300);
              }, 3000);
            } else {
              done();
            }
          }
        }).then(action => {
          this.$message({
            type: 'info',
            message: 'action: ' + action
          });
        });
      },
    }
  }
</script>
```
:::

:::tip
The content of MessageBox can be `VNode`, allowing us to pass custom components. When opening the MessageBox, Vue compares new `VNode` with old `VNode`, then figures out how to efficiently update the UI, so the components may not be completely re-rendered ([#8931](https://github.com/ElemeFE/element/issues/8931)). In this case, you can add a unique key to `VNode` each time MessageBox opens: [example](https://jsfiddle.net/zhiyang/ezmhq2ef).
:::

### Use HTML String

`message` supports HTML string.

:::demo Set `dangerouslyUseHTMLString` to true and `message` will be treated as an HTML string.

```html
<template>
  <el-button type="text" @click="open">Click to open Message Box</el-button>
</template>

<script>
  export default {
    methods: {
      open() {
        this.$alert('<strong>This is <i>HTML</i> string</strong>', 'HTML String', {
          dangerouslyUseHTMLString: true
        });
      }
    }
  }
</script>
```
:::

:::warning
Although `message` property supports HTML strings, dynamically rendering arbitrary HTML on your website can be very dangerous because it can easily lead to [XSS attacks](https://en.wikipedia.org/wiki/Cross-site_scripting). So when `dangerouslyUseHTMLString` is on, please make sure the content of `message` is trusted, and **never** assign `message` to user-provided content.
:::

### Distinguishing cancel and close

In some cases, clicking the cancel button and close button may have different meanings.

:::demo By default, the parameters of Promise's reject callback and `callback` are 'cancel' when the user cancels (clicking the cancel button) and closes (clicking the close button or mask layer, pressing the ESC key) the MessageBox. If `distinguishCancelAndClose` is set to true, the parameters of the above two operations are 'cancel' and 'close' respectively.

```html
<template>
  <el-button type="text" @click="open">Click to open Message Box</el-button>
</template>

<script>
  export default {
    methods: {
      open() {
        this.$confirm('You have unsaved changes, save and proceed?', 'Confirm', {
          distinguishCancelAndClose: true,
          confirmButtonText: 'Save',
          cancelButtonText: 'Discard Changes'
        })
          .then(() => {
            this.$message({
              type: 'info',
              message: 'Changes saved. Proceeding to a new route.'
            });
          })
          .catch(action => {
            this.$message({
              type: 'info',
              message: action === 'cancel'
                ? 'Changes discarded. Proceeding to a new route.'
                : 'Stay in the current route'
            })
          });
      }
    }
  }
</script>
```
:::

### Centered content
Content of MessageBox can be centered.

:::demo Setting `center` to `true` will center the content

```html
<template>
  <el-button type="text" @click="open">Click to open Message Box</el-button>
</template>

<script>
  export default {
    methods: {
      open() {
        this.$confirm('This will permanently delete the file. Continue?', 'Warning', {
          confirmButtonText: 'OK',
          cancelButtonText: 'Cancel',
          type: 'warning',
          center: true
        }).then(() => {
          this.$message({
            type: 'success',
            message: 'Delete completed'
          });
        }).catch(() => {
          this.$message({
            type: 'info',
            message: 'Delete canceled'
          });
        });
      }
    }
  }
</script>
```
:::

### Global method

If Element is fully imported, it will add the following global methods for Vue.prototype: `$msgbox`, `$alert`, `$confirm` and `$prompt`. So in a Vue instance you can call `MessageBox` like what we did in this page. The parameters are:
- `$msgbox(options)`
- `$alert(message, title, options)` or `$alert(message, options)`
- `$confirm(message, title, options)` or `$confirm(message, options)`
- `$prompt(message, title, options)` or `$prompt(message, options)`

### Local import

If you prefer importing `MessageBox` on demand:

```javascript
import { MessageBox } from 'element-ui';
```

The corresponding methods are: `MessageBox`, `MessageBox.alert`, `MessageBox.confirm` and `MessageBox.prompt`. The parameters are the same as above.

### Options

| Attribute      | Description          | Type      | Accepted Values       | Default  |
|---------- |-------------- |---------- |--------------------------------  |-------- |
| title | title of the MessageBox | string | — | — |
| message | content of the MessageBox | string | — | — |
| dangerouslyUseHTMLString | whether `message` is treated as HTML string | boolean | — | false |
| type | message type, used for icon display | string | success / info / warning / error | — |
| iconClass | custom icon's class, overrides `type` | string | — | — |
| customClass | custom class name for MessageBox | string | — | — |
| callback | MessageBox closing callback if you don't prefer Promise | function(action), where action can be 'confirm', 'cancel' or 'close', and `instance` is the MessageBox instance. You can access to that instance's attributes and methods | — | — |
| showClose | whether to show close icon of MessageBox | boolean | — | true |
| beforeClose | callback before MessageBox closes, and it will prevent MessageBox from closing | function(action, instance, done), where `action` can be 'confirm', 'cancel' or 'close'; `instance` is the MessageBox instance, and you can access to that instance's attributes and methods; `done` is for closing the instance | — | — |
| distinguishCancelAndClose | whether to distinguish canceling and closing the MessageBox | boolean | — | false |
| lockScroll | whether to lock body scroll when MessageBox prompts | boolean | — | true |
| showCancelButton | whether to show a cancel button | boolean | — | false (true when called with confirm and prompt) |
| showConfirmButton | whether to show a confirm button | boolean | — | true |
| cancelButtonText | text content of cancel button | string | — | Cancel |
| confirmButtonText | text content of confirm button | string | — | OK |
| cancelButtonClass | custom class name of cancel button | string | — | — |
| confirmButtonClass | custom class name of confirm button | string | — | — |
| closeOnClickModal | whether MessageBox can be closed by clicking the mask | boolean | — | true (false when called with alert) |
| closeOnPressEscape | whether MessageBox can be closed by pressing the ESC | boolean | — | true (false when called with alert) |
| closeOnHashChange | whether to close MessageBox when hash changes | boolean | — | true |
| showInput | whether to show an input | boolean | — | false (true when called with prompt) |
| inputPlaceholder | placeholder of input | string | — | — |
| inputType | type of input | string | — | text |
| inputValue | initial value of input | string | — | — |
| inputPattern | regexp for the input | regexp | — | — |
| inputValidator | validation function for the input. Should returns a boolean or string. If a string is returned, it will be assigned to inputErrorMessage | function | — | — |
| inputErrorMessage | error message when validation fails | string | — | Illegal input |
| center | whether to align the content in center | boolean | — | false |
| roundButton | whether to use round button | boolean | — | false |
