Try this: 

widget.model == 'report.pos.order'

Have you tried using the code below?

widget.modelName == 'report.pos.order'

Hi, try also depending on where you are:

1. this.value.model

2. this.state.model

If it doesn't help,

1. add a few loggers, like console.log(this), console.log(widget)

2. Press F12 --> choose console --> reload page

3. You would see a js object with all available attributes. One of those would definitely have model or res_model