Question about .on method

I'm new to node.js as well, but I'll try.

The first parameter in the double quotes is not a variable. It just identifies the event type that will trigger the callback function that is the second parameter. In other words. The callback function is run on response's "error" event. Just like "data" and "end". The callback function receives an error object as a parameter but you can name that anything, like 'err' or whatever.

If you are unfamiliar with the arrow function syntax, there is a short course about it in treehouse.

These are actually "arguments" supplied to the .on() method, not parameters. A parameter would be the variable inside the method declaration in the https object library. You are passing these arguments into the method to be used in the parameters in the function logic that is run "behind the scenes"

The first "error" is an argument passed in, and the logic in the .on() method will use that to determine the type of event you are trying to handle., and use it's logic within itself accordingly. We cannot see this logic, as .on() is a method on the https object we imported in our require() statement. You would have to go to the node.js docs, and find it to view the logic for the method.

The second argument is the entire callback function. The error variable here is the object supplied to the callback function from the .on() method. You could declare this as anything you want, i.e. err, e, foo, bar. Either way, the object itself does not change, it is still an error object. It just changes the variable name you use to reference the object within the callback function.'

Example:

// This is the same...
request.on("error", error =>{console.error(`There was an error trying to process your request: ${error.message}`);})
// as this...
request.on("error", foo =>{console.error(`There was an error trying to process your request: ${foo.message}`);})
// and this
request.on("error", (foo) =>{console.error(`There was an error trying to process your request: ${foo.message}`);})
// and this
request.on("error", function(foo){
    console.error(`There was an error trying to process your request: ${foo.message}`);
})