Implement MessageCommand Interfaces per Enumeration

[stricklandrbls]

Issue

The MessageCommand enumeration represents the potential message types that are communicated back and forth, via websockets, between the dataEditorClient object and its WebViewPanel.

Svelte components append an event listener to the DOM that listen for different enumerations of MessageCommand and act accordingly. Though, developers are unable to confidently index into the msg.data.data object because that portion of the message is always initialized inline.

Example

vscode.postMessage({
    command: MessageCommand.testCommand ,
    data: {
        a: 'a',
        b: 'b',
    }
})

Because of this, there is no index / intellisense relating to the data object.

Solution

Create and implement an interface, type, or data structure that would allow a developer to type cast the data portion of the VSCode message and accurately determine the structure of each MessageCommand enumeration.

Example
Receiving a message.

  window.addEventListener('message', (msg) => {
    switch (msg.data.command) {
      case MessageCommand.test:
        const data = msg.data.data as TestCommand
        ...