We've got a very simple node express application here. Package.json says on start, run node index.js. Index.js just says, any incoming requests you get to the root path, just respond with "Hello, World," and the current time. I'm going to go ahead and listen on port 3000.
If we run npm start and we go to local host 3000 here, we see "Hello, World, the current time is this." The problem we want is we don't want to run this locally, we want to deploy this so anyone in the world can visit that endpoint and find out what time it is.
To do that, we're going to type npm install -g now, which is going to install the Now package from a company called ZEIT globally. When you install something globally on npm, that means you can just type, if there's a binary exposed like there is for now, you can just type that command in any folder and it'll attempt to run.
What happens if I type now in a folder that has a package.json file? Something pretty simple and amazing. It's going to generate a URL for me, which you can see here, and it's going to copy it to the clipboard for me. It's going to upload my entire project to a remote Web server.
Then it's going to run npm install, so it's going to pull down whatever specification I had, in this case, it was just express. Then it's going to run npm run build, just in case you have a Build step. I don't, but I wanted to stick that in there so you could see that it runs. Then it'll run npm start. That'll run your Start script.
Then if you go to the URL that it generates for you, you can hit Enter in your browser, there's your application and it's currently running and it's live. I can refresh it and watch the time refresh. This is live in production right now.
Now, something cool about this URL. This is the name of my project, and this is a unique key that it generated based on, like, the state of my application right now. It looks at my package.json, and it looks at my code.
It says, OK, awesome. If you deploy this package against this code, using now, that's the URL that you get. I can show you that that's true by running ZEIT now again. Pay attention, it's Q-H-O-O-M something.
If I run Now again, we're not going to see it do npm install and npm run build and npm start, it's actually just going to give us the same URL again. This is using a certain property of immutable data structures.
It's actually saying that this deployed instance is like a pure function of this particular named project with the current state of this code. No matter how many times I deploy the current state, it's always going to return the same deployment instance that I can get to via that URL.
It's going to be up forever unless I choose to take it down, so if you're watching this in three years, if you type in this URL, then, in theory, this should just work. How do I change stuff, then? What does that mean in the world of immutability?
The first thing you want to ask is, "OK, well, how is change handled?" Let's try to change. Let's say, instead of "Hello, World," our marketing department's come back and said, "It turns out 'Hello, World' is overdone. The new thing is 'Hello, Universe.'"
OK, great, so we make that change. We've run now. You can see it's actually giving us a new URL, because the package.json file with this code, which is different from the previous code, means that our input has changed, which means that our output has changed.
Now, if we go to this endpoint, we see "Hello, Universe." Note that this endpoint is still here. I can still hit Refresh and get "Hello, World." Isn't that like super inefficient? Isn't this using up a ton of system resources?
No, with modern containerization and stuff, it's easy for them to, this URL doesn't get any requests for a while, because this is now, like, the new canonical endpoint for this project, they can just put this one to sleep.
It's still available, it just means that the next time somebody does submit a request to it, it is going to just take a few extra seconds to warm up. Let's look at one other feature here. Sometimes, if we're running things locally, we want to have a different sort of setup than we do if we're running them remotely.
Now offers a nice little escape hatch here. If we define a script called start, and a script called now start, then when we've run it on Now, it'll ignore start and it'll run now start. The same for build, if we define a now build, echo now build step went here.
If I then run Now, we're going to see, now that our dependencies have been installed, run now build and then run now start. That's just useful, like, we're not doing anything special with it here.
If you want your dev to run with certain environment variables, for instance, and your prod to run with other ones or something like that, we can dig a little bit more deeper into that in future lessons. There is an escape hatch, and there is a way for you to have Now specific start in build scripts.