declare.ts

declare var Ext: any;

ext-create.ts

const myGrid = Ext.create<MyApp.grids.Users>("SchedulerApp.view.UserGrid");
const currentSelection = myGrid.getSelectionModel().getSelection(); 
// currentSelection is a type of Ext.selection.Model

// myapp.view.users.ts
Ext.define<MyApp.grids.Users>("MyApp.view.Users", {
    extend: "Ext.grid.Panel",   
    selModel: {
        mode: "MULTI"
    },
    columns: [
        Ext.create<any>("MyApp.columns.shared.Name", { filter: { type: "owner" } })
    ]
}

// myapp.grids.d.ts
declare module MyApp.grids {
    export class Users extends Ext.grid.Panel {      
    }
}

// ext.grid.d.ts
declare module Ext.grid {
    export interface Panel extends Ext.Component {
        getSelectionModel?(): Ext.selection.Model;
        on?(eventName: string, callback: any): void;
        setDisabled?(val: boolean): void;
        getStore?(): Ext.data.Store;
    }
}

declare module Ext {
  export interface Component {
      extend?: string,
      selModel?: Ext.selection.Model,
      columns?: any[]
  }
}

ext-type.ts

declare module Ext {
    export function create<T>(className: string, config?: T): T;
    export function define<T>(className: string, config: T);
}

ext.js

Ext.define("MyApp.view.CustomersGrid", {
    extend: "Ext.grid.Panel",  
    selModel: {
        selType: "rowmodel",
        mode: "SINGLE"
    },
    columns: [{
        text: 'Name',
        flex: 1,
        dataIndex: 'name'
    }, {
        text: 'Location',        
        dataIndex: 'location'
    }],
    initComponent: function () {
    }
}

ts-class.js

Ext.define("MyApp.panel.Grid", {
   constructor(config) {
     this.callParent(arguments);
   }
})

ts-class.ts

declare module MyApp.panel {
    export class Grid {
      constructor(config: any) {
         super();
      }
    }
}