Basics: Types

Variables in JavaScript do not have a “fixed type”.

Once you assign a value of some type to a variable, you can later reassign the variable to host a value of any other type, without any issue.

In JavaScript, we have 2 main kinds of types: primitive types and object types.

Primitive types are:

  • numbers
  • strings
  • booleans
  • symbols

And two special types: null and undefined.

Any value that’s not of a primitive type (a string, a number, a boolean, null, or undefined) is an object.

We’ll talk more about objects later on.

The main difference I mention now about primitive types and objects is that objects are passed by reference, while primitive types are passed by value. This is a concept that will be useful when we’ll introduce functions.

Lessons this unit:

0: Introduction
1: Literals, identifiers and variables
2: Comments
3: The difference between let, const and var
4: ▶︎ Types
5: Operators and expressions
6: Let's start with arithmetic operators
7: The assignment operator
8: Operators precedence
9: Strings
10: Numbers
11: Semicolons, white space and sensitivity