pure javascript TextDocumentContentProvider for vscode

provider.js

var vscode = require('vscode');

class PostWindowContentProvider {
    constructor() {
        this._onDidChange = new vscode.EventEmitter();
    }
    provideTextDocumentContent(uri) {
        return 'Hi I am some content.';
    }
    get onDidChange() {
        return this._onDidChange.event;
    }
    update(uri) {
        this._onDidChange.fire(uri);
    }
}