Introduction to Node.js -  Comparing the Browser and Node.js. In this video, I'm going to cover the fundamental difference between the Browser and Node.js. I'm going to begin in the Chrome Console, and I will start by typing 'confirm'. Inside of the confirm, parentheses, I will pass through the following confirmation message, "Would you like to continue?"

I will hit 'Enter' to execute. Now on the screen, the confirmation pop-up has appeared. I'm going to hit 'OK'. So, how would this work using Node? I'm going to transition to the Theia lab environment, and I already have an index.js file created. In the file, I will type the same confirm command along with the same message.

Now I'm going to execute the code in this file. In order to do so, I need to type in the terminal, 'node' and the relative path to the file along with the file's name. Since the Terminal is in the same working directory as where the index.js file is located, I just need to type index.js. By using this command, the node runtime environment will read this file, convert the JavaScript code to machine code, and then execute the code. I will go ahead and hit 'Enter' on my keyboard to run the command. Now there is a ReferenceError:  confirm is not defined.

Now to investigate this a little further, I'm going to go back to the Chrome Console, and instead of the console, I will type 'console.log(window)'  and hit 'Enter'. And there is the window object which represents the entirety of the browser. Now I'm going to also console.log(this)  and hit 'Enter'. And this also refers to the window object. If I expand the object, there is the confirm method. I am going to transition back to Theia. 

Now in the Theia lab environment, I'm going to comment out the confirm message. And I'm going to console.log(window). I will clear my terminal and run the node: index.js command again. And now there's a new error message:  window is not defined. To take this further, I'm going to comment out the console.log, and I'm going to console.log(this). And I will clear my terminal again and execute the index.js file. And now in the terminal, there's an empty object. There's some scoping involved. But right now, this references the object node creates for any module exports. Currently, there are no modules being used  hence the empty object. And the discussion about modules is out of scope for this video.

Now going back to when I console.log the window, it came out undefined. Why is that?  Node is a independent JavaScript runtime that runs outside of the browser. Therefore, there is no window. Because there is no window, there is no dumb or Web APIs. The confirm command is a Web API and it will only work within the browser. It doesn't exist in node. Node replaces Web APIs with built in modules that offer different features and functionality. And that's it. Thanks for watching @CloudAcademy.