How JavaScript Works—Execution Context

Introduction

In this lesson, we will learn about how JavaScript works and how JavaScript code is executed behind the scenes. We will also answer two questions:

• Is JavaScript a synchronous or an asynchronous language?

• Is JavaScript a single-threaded or a multi-threaded programming language?

Execution context

Everything in JavaScript happens inside an execution context. You can think of this execution context as a big container in which the whole JavaScript code is executed. An execution context consists of two components: the variable environment and the thread of execution.

Below is a simple illustration to help you understand the design of the execution context.

Let's go over each of those components:

• Variable environment: This first component (also known as the memory component) is an environment where all the variables and functions are stored as key-value pairs. For example, let's assume we have a variable a, whose value is set to 10. It will be held in the variable environment ...