Parsing and formatting times

Note that the date properties of the objects in our runs array are strings and not date objects. This is a problem because xScale, as with all time scales, expects its data values to be date objects. Fortunately, D3 provides us an easy way to convert strings to dates and vice versa. We'll use a specially formatted string, based on the documentation (https://github.com/d3/d3-time-format#locale_format), to tell D3 how to parse the date string properties of the objects in our runs array into actual JavaScript date objects. Add the following at the end of app.js:

//this format matches our data in the runs array
var parseTime = d3.timeParse("%B%e, %Y at %-I:%M%p"); 
console.log(parseTime('October 3, 2017 at 6:00PM'));
var formatTime = d3.timeFormat("%B%e, %Y at %-I:%M%p");
//this format matches our data in the runs array 
console...