Uncaught TypeError: Reflux.listenTo is not a function

Question

My code looks like this:

mixins: [Reflux.listenTo(ItemStore,"onChange")],

....

onChange: function(items) {
    this.setState({items: items});
},

when I run npm start and on browser when I look into console, the error refers to the "mixins" line. If I change the string within quotation "onChange", I still get the same error.