Key Concepts

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Node.js REPL

//node is typed in the console to access REPL $ node //the > indicates that REPL is running // anything written after > will be evaluated > console.log("HI") // REPL has evaluated the line and has printed out HI HI

Node.js comes with REPL, an abbreviation for read–eval–print loop. REPL contains three different states:

*a read state where it reads the input from a user, *the eval state where it evaluates the user’s input *the print state where it prints out the evaluation to the console.

After these states are finished REPL loops through these states repeatedly. REPL is useful as it gives back immediate feedback which can be used to perform calculations and develop code.

What is the Back-end?
Lesson 1 of 2
  1. 1
    In this lesson, we’ll explain what makes up the back-end of a web application or website. The back-end can feel very abstract, but it becomes clearer when we explain it in terms of the front-end! T…
  2. 2
    We talked about how the front-end consists of the information sent to a client so that a user can see and interact with a website, but where does the information come from? The answer is a _web ser…
  3. 3
    When a user navigates to, their request specifies the URL but not the filename for today’s Google Doodle . The web application’s back-end will need to hold the logic for deciding which …
  4. 4
    You’ve probably heard that data is a big deal. By some measures, 90% of the world’s data has been generated in just the past two years! From a stored credit card number on an e-commerce site to the…
  5. 5
    When a user navigates to a specific item for sale on an e-commerce site, the price listed for that item is stored in a database, and when they purchase it, the database will need to be updated with…
  6. 6
    Two other concepts we’ll want our server-side logic to handle are authentication and authorization. Authentication is the process of validating the identity of a user. One technique for aut…
  7. 7
    Unlike the front-end, which must be built using HTML, CSS, and JavaScript, there’s a lot of flexibility in which technologies can be used in order to create the back-end of a web application. Devel…
  8. 8
    In order to deliver the front-end of a website or web application to a user, a lot needs to happen behind the scenes on the back-end! Understanding what makes up the back-end can be overwhelming be…

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