I am trying to customized the zoom widget, i.e. i have created my own zoom in/out template, and now i want to invoke the zooming functionalities, but when i looked into the codes for zoom widget(zoom.js) the code is refererring this.viewModel.zoomOut();, so just would like to know that, from where it will get the reference of this.viewModel , i didnot find anywhere, in my case it comes as "undefined". any clue/pointer on this.