You need to know the basics of JavaScript, including the following:

• An understanding of some of the primitive JavaScript types, such as string, number, Boolean, null, and undefined
• An understanding of how to create variables and reference them, including arrays and objects
• An understanding of how to create functions and call them
• An understanding of how to create conditional statements with the if and else keywords

You need to know the basics of HTML, including the following:

• An understanding of basic HTML tags, such as div, ul, p, a, h1, and h2, and how to compose them together to create a web page
• An understanding of how to reference a CSS class to style an HTML element

An understanding of basic CSS is also helpful, but not essential:

• How to size elements and include margins and padding
• How to position elements
• How to color elements

You will need the following technologies installed on your computer:

• Google Chrome: This can be installed at https://www.google.com/chrome/.
• Node.js and npm: These are used throughout this book. You can install them at https://nodejs.org/en/download/. If you already have these installed, make sure that Node.js is at least version 8.2 and that npm is at least version 5.2. 
• TypeScript: This can be installed via npm by entering the following command in a terminal:

npm install -g typescript

• Visual Studio Code: You'll need this to write React and TypeScript code. This can be installed from https://code.visualstudio.com/.