01. Execution Context

When JS code executes, it always happens within certain execution context. For each of types of executable code, there’s an execution context. There are 4 types of executable code in JS:

• Global code,

  • Content of <script /> elements

  • Non-module code

• Module code,

• • Content of <script type="module" />

  • Module code

• Function code,

  • Content of event attributes (e.g. <p onclick="...">)

  • Anything that’s executed directly within a function,

• Eval code.

  • Text that’s supplied to a built-in eval function is parsed as Eval code

As you can see, execution contexts can logically form a stack:

1. First there might be Global code or Module code with its own execution context;

2. That code might call a function, with its own execution context;

3. That function could call another function, and so on and so forth.

4. Even if function is calling itself recursively, a new execution context is being entered with every invocation.