# JavaScript events

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This section shows you how to create a `WKUserScript` from a JavaScript context to:

-   Pass the current environment parameters to the web view.
-   Terminate the current session and process commands for callback functions.
-   Handle messages that the host app should process for handoff events.

## Inject environment parameters into WebView

To pass the current environment parameters to the web view, create a `WKUserScript`.

Here is an example in iOS Swift.

**Note**: This example only works with Mobile SDK.

```swift
let userContentController = WKUserContentController()
let webviewConfig = WKWebViewConfiguration()
webviewConfig.userContentController = userContentController

let injectScriptStr = """
window.zoomCampaignSdkConfig = window.zoomCampaignSdkConfig || {

    language: 'user language',
    firstName: 'user first name',
    lastName: 'user last name',
    nickName: 'user nick name',
    address: 'user address',
    company: 'user company',
    email: 'user email',
    phoneNumber: 'user phone number'
};

"""
let injectScript = WKUserScript(source: injectScriptStr, injectionTime: .atDocumentStart, forMainFrameOnly: false)
userContentController.addUserScript(injectScript)
```

> **Supported languages for language**
>
> `en-US`, `da-DK`, `de-DE`, `en-AU`, `en-GB`, `en-NZ`, `es-ES`, `es-MX`, `es-US`, `fr-CA`, `fr-FR`, `id-ID`, `it-IT`, `ja-JP`, `ko-KR`, `nl-NL`, `pl-PL`, `pt-BR`, `pt-PT`, `ro-RO`, `ru-RU`, `sv-SE`, `tr-TR`, `vi-VN`, `zh-CN`, and `zh-TW`

## Handle exit callback functions

To handle the termination of the current session and process commands from the JavaScript context, create a `WKUserScript`.

Here is an example in iOS Swift.

```swift
let exitHandlerScriptStr = """
window.addEventListener('zoomCampaignSdk:ready', () => {
    if (window.zoomCampaignSdk) {
        window.zoomCampaignSdk.native = {
            exitHandler: {
                handle: function() {
                    window.webkit.messageHandlers.zoomLiveSDKMessageHandler.postMessage('close_web_vc');
                }
            },
            commonHandler: {
                handle: function(e) {
                    window.webkit.messageHandlers.commonMessageHandler.postMessage(JSON.stringify(e));
                }
            }
        }
    }
})
"""
let exitScript = WKUserScript(source: exitHandlerScriptStr, injectionTime: .atDocumentStart, forMainFrameOnly: false)
userContentController.addUserScript(exitScript)
```

## Handle handoff events

To handle messages from the JavaScript context that the host app should process for handoff events, create a `WKUserScript`.

Here is an example in iOS Swift.

```swift
let supportHandoffScriptStr = """
window.addEventListener('support_handoff', (e) => {
    window.webkit.messageHandlers.support_handoff.postMessage(JSON.stringify(e.detail));
});

"""
let supportHandoffScript = WKUserScript(source: supportHandoffScriptStr, injectionTime: .atDocumentStart, forMainFrameOnly: false)
userContentController.addUserScript(supportHandoffScript)
```