IE11 doesn't support several ES6 features, including lambda functions and template literals.
A rough equivalent that should work is:
myApp.run(function(EventTitle, moment) {
EventTitle.weekView = function(event) {
return moment(event.startsAt).format('hh:mm') + " " + event.title;
};
});
However, there are some ways in which arrow functions do not work in the same way as regular functions. You'll need to watch for the use of this
keywords, for example.
Alternatively, if you use a transpiler like Babel (or a transpiled language like TypeScript), you can use newer language features like your original code, and automatically generate JavaScript code that will run in browsers that don't support those features.