You don’t need to guess the correct data type required in your program. Both undefined and null are values that represent nothing, and other programming languages usually only have one, and that is null. A constant variable is a variable that doesn’t change its value as long as the program is running. In other programming languages, changing the value of a constant will produce an error. JavaScript is a programming language that allows you to implement complex functionalities on web pages. JavaScript is a programming language that adds interactivity to your website.

  • This is the command you use to find out which directory your terminal is currently on.
  • There are times when you need to store a value that never changes in a variable.
  • We’re also going to leave out HTML, CSS, and using JavaScript in the browser.
  • JavaScript considers the local scope variable to be a different variable.

The else statement is used to run code only when the if statement is not fulfilled. You need to modify the original array using the methods explained in this section. JavaScript remembers the position JavaScript Lessons of the elements within an array. These operators are pretty straightforward, so you can try them on your own. To add the two numbers properly, you need to convert the x variable into an integer.

JavaScript Modules

If you omit the break keyword, then the code execution will continue to the next block. First, you need to pass an expression to be evaluated by the switch statement into the parentheses. In the example, the age variable is passed as an argument for evaluation. You’ve seen some examples of using the plus + operator to join multiple strings and add two numbers together.

  • Both undefined and null are values that represent nothing, and other programming languages usually only have one, and that is null.
  • A key must also be unique, so you can’t use the same key twice in the same object.
  • The Node.js software you downloaded previously is the tool that processes JavaScript code.
  • To better prepare you for the real world, we have 17 projects inspired by popular products.
  • When we call the checkAge() function the first time, the value of age argument is greater than 18, so JavaScript executes the return statement inside the if block.
  • Visit Mozilla Corporation’s not-for-profit parent, the Mozilla Foundation.Portions of this content are ©1998–2024 by individual mozilla.org contributors.

A key must also be unique, so you can’t use the same key twice in the same object. This is certainly better as you can group related data about the book together, but you have no way to add context to the value. Instead, it offers improvements to the way you write a function in JavaScript. Back in Chapter 7, recall that we briefly explored the difference between undefined as the “default” empty value and null as the “intentional” empty value. Here, the while loop will repeatedly print the value of i as long as i is less than 6.

Variable scope

The log() function is used to “print” whatever you put inside the parentheses. We’re also going to leave out HTML, CSS, and using JavaScript in the browser. This tutorial focuses only on JavaScript as a programming language and uses the terminal to run the code. Next, we’ll turn our attention to strings — this is what pieces of text are called in programming.

If you want to print the numbers before the text, then you need to move the corresponding console.log() lines to the top. Each statement is an expression of some action that needs to be carried out by the software that executes the code. There are lots of things you can do with the console, but these 7 commands would be enough because we only need it to run JavaScript code.