Before we proceed with ES6 classes, let's refresh our knowledge of JavaScript data types, constructors, and inheritance. While learning classes, we will be comparing the syntax of constructors and prototype-based inheritance with the syntax of classes. Therefore, it is important to have a good grasp of these topics.
JavaScript variables hold (or store) data (or values). The type of data variables that they hold is called the data type. In JavaScript, there are seven different data types: number, string, Boolean, null, undefined, symbol, and object.
When it comes to holding objects, variables hold the object reference (that is, the memory address) instead of the object itself. If you're coming from a C/C++ background, you can relate them to pointers, but not exactly.
All data types other than objects are called primitive data types.