URN vs. URL vs. URI

Uniform Resource Identifier (URI) : Identify
A compact sequence of characters that identifies an abstract or physical resource. Encompases URN's and URL's (and URC's).

Example: "www.google.com", "http://www.google.com"

Uniform Resource Name (URN) : Uniquely name
Identifies a resource by a unique and persistent name, but doesn't necessarily tell you how to locate it on the internet. 

Example use: 6e8bc430-9c3a-11d9-9669-0800200c9a66

Unified Resource Location (URL) : Locate
Contains information about how to fetch a resource from its location. URL's ALWAYS start with protocol. 
Example use: "http://www.google.com"

So if I want to be 'that guy', when should I use which terms? 
Use URI's for most everything, unless it includes protocol ('http://', 'https://', etc) in which case be 'that guy' and say it's a URL. 

Source
https://danielmiessler.com/study/url-uri/

Dependency Injection

What is Dependency Injection

A technique of 'injecting' the dependencies of one object to another.

Not this:
function a (id) {
         return b(id)
                       .then(response => response.json())
}

This:
function a (b, id) {
          return b(id)
                       .then(response => response.json())
}

Why use it?

It's more explicit, easier to read and provides more control over inputs...but practically speaking, it makes it easier to unit test your application. There are many ways to test your application, but dependency injection is a common and well known design pattern, well documented and can (for the most part) be implemented with most languages.

Source
https://www.youtube.com/watch?v=0X1Ns2NRfks
https://en.wikipedia.org/wiki/Dependency_injection