# Developers

- [JavaScript](/developers/javascript.md): Add functionality in your app via JavaScript
- [Develop locally](/developers/javascript/develop-locally.md): How to build your JavaScript app
- [SDK](/developers/javascript/sdk.md): @myjsblock/sdk
- [Core](/developers/javascript/sdk/core.md): Core JavaScript features
- [JS Data](/developers/javascript/sdk/js-data.md): Data is the driving force behind your app. Integrate your custom JavaScript code with the web services in your app using these functions.
- [Media](/developers/javascript/sdk/media.md): Allow users to share device media with your custom JavaScript code.
- [Navigation](/developers/javascript/sdk/navigation.md): Give the user a tour of your beautiful app using the navigation functions.
- [Notification](/developers/javascript/sdk/notification.md): Engage with your users by using our notification and dialog functions.
- [User](/developers/javascript/sdk/user.md): Develop user-specific features to interact with your users on a closer level.
- [CLI](/developers/javascript/cli.md): @myjsblock/cli
- [CLI Token and Secret](/developers/javascript/cli/cli-token-and-secret.md): This article explains where to find and/or renew the token and secret required to enable updating the JavaScript block's code via the Command Line Interface (CLI).
- [Errors](/developers/javascript/cli/errors.md)
- [CONFIG\_PROPERTIES\_INVALID](/developers/javascript/cli/errors/config_properties_invalid.md): Config properties are invalid
- [CONFIG\_VALUES\_INVALID](/developers/javascript/cli/errors/config_values_invalid.md): Config values are invalid
- [ENTRY\_FILE\_NOT\_FOUND](/developers/javascript/cli/errors/entry_file_not_found.md): The entry file: {entryFile}, is not found in: {outputDirectory}
- [OUTPUT\_DIRECTORY\_IS\_EMPTY](/developers/javascript/cli/errors/output_directory_is_empty.md): The configured output directory is empty: {{outputDirectory}}
- [OUTPUT\_DIRECTORY\_NOT\_FOUND](/developers/javascript/cli/errors/output_directory_not_found.md): The configured output directory is not found: {{outputDirectory}}
- [TOKEN\_SECRET\_NOT\_PROVIDED](/developers/javascript/cli/errors/token_secret_not_provided.md): No secret or token provided.
- [TOKEN\_SECRET\_NOT\_VALID](/developers/javascript/cli/errors/token_secret_not_valid.md): The token or secret is not valid.
- [Migrate from old Custom JS](/developers/javascript/migrate-from-old-custom-js.md): Actions required for classic apps to start using the new JS block
- [Web services](/developers/web-services.md): Connect to external web services to add data to your app