Activation Events

Activation Events is a set of JSON declarations that you make in the activationEvents field of package.json Extension Manifest. Your extension becomes activated when the Activation Event happens. Here is a list of all available Activation Events:

We also provide a reference of all fields in the package.json extension manifest.

onLanguage

This activation event is emitted and interested extensions will be activated whenever a file that resolves to a certain language gets opened.

...
"activationEvents": [
    "onLanguage:python"
]
...

The onLanguage event takes a language identifier value.

Multiple languages can be declared with separate onLanguage entries in the activationEvents array.

"activationEvents": [
    "onLanguage:json",
    "onLanguage:markdown",
    "onLanguage:typescript"
]
...

onCommand

This activation event is emitted and interested extensions will be activated whenever a command is being invoked:

...
"activationEvents": [
    "onCommand:extension.sayHello"
]
...

onDebug

This activation event is emitted and interested extensions will be activated before a debug session is started:

...
"activationEvents": [
    "onDebug"
]
...

onDebugInitialConfigurations

onDebugResolve

These are two more fine-grained onDebug activation events:

onDebugInitialConfigurations is fired just before the provideDebugConfigurations method of the DebugConfigurationProvider is called.
onDebugResolve:type is fired just before the resolveDebugConfiguration method of the DebugConfigurationProvider for the specified type is called.

Rule of thumb: If activation of a debug extension is lightweight, use onDebug. If it is heavyweight, use onDebugInitialConfigurations and/or onDebugResolve depending on whether the DebugConfigurationProvider implements the corresponding methods provideDebugConfigurations and/or resolveDebugConfiguration. See Using a DebugConfigurationProvider for more details on these methods.

workspaceContains

This activation event is emitted and interested extensions will be activated whenever a folder is opened and the folder contains at least one file that matches a glob pattern.

...
"activationEvents": [
    "workspaceContains:**/.editorconfig"
]
...

onFileSystem

This activation event is emitted and interested extensions will be activated whenever a file or folder from a specific scheme is read. This is usually the file-scheme, but with custom file system providers more schemes come into place, e.g ftp or ssh.

...
"activationEvents": [
    "onFileSystem:sftp"
]
...

onView

This activation event is emitted and interested extensions will be activated whenever a view of the specified id is expanded:

...
"activationEvents": [
    "onView:nodeDependencies"
]
...

onUri

This activation event is emitted and interested extensions will be activated whenever a system-wide Uri for that extension is opened. The Uri scheme is fixed to either vscode or vscode-insiders. The Uri authority must be the extension's identifier. The rest of the Uri is arbitrary.

...
"activationEvents": [
    "onUri"
]
...

If the vscode.git extension defines onUri as an activation event, it will be activated in any of the following Uris are open:

vscode://vscode.git/init
vscode://vscode.git/clone?url=https%3A%2F%2Fgithub.com%2FMicrosoft%2Fvscode-vsce.git
vscode-insiders://vscode.git/init (for VS Code Insiders)

onWebviewPanel

This activation event is emitted and interested extensions will be activated whenever VS Code needs to restore a webview with the matching viewType.

For example, the declaration of onWebviewPanel below:

"activationEvents": [
    ...,
    "onWebviewPanel:catCoding"
]

will cause the extension to be activated when VS Code needs to restore a webview with the viewType: catCoding. The viewType is set in the call to window.createWebviewPanel and you will need to have another activation event (for example, onCommand) to initially activate your extension and create the webview.

Start up

The * activation event is emitted and interested extensions will be activated whenever VS Code starts up. To ensure a great end user experience, please use this activation event in your extension only when no other activation events combination works in your use-case.

...
"activationEvents": [
    "*"
]
...

Note: An extension can listen to multiple activation events, and that is preferable to listening to "*".

Note: An extension must export an activate() function from its main module and it will be invoked only once by VS Code when any of the specified activation events is emitted. Also, an extension should export a deactivate() function from its main module to perform cleanup tasks on VS Code shutdown. Extension must return a Promise from deactivate() if the cleanup process is asynchronous. An extension may return undefined from deactivate() if the cleanup runs synchronously.