Execution context (EC) is defined as the environment/scope in which JavaScript code is executed.
By environment means the value of this, variables, objects, and functions JavaScript code has access to, constitutes it’s environment.
In JS Environmentis a data structure that provides that storage space to variables.

• Execution context types

  1. Global execution context (GEC) The default environment in which code is executed for the first time.
  2. Functional execution context (FEC) Whenever the flow of execution enters a function body.
  3. Eval: Execution context inside eval function.

The JavaScript interpreter in a browser is implemented as a single thread.
What this actually means is that only 1 thing can ever happen at one time in the browser, with other actions or events being queued in what is called the Execution Stack.

• There are 5 key points to remember about the execution stack

  1. Single threaded.
  2. Synchronous execution.
  3. 1 Global context.
  4. Infinite function contexts.
  5. Each function call creates a new execution context, even a call to itself.

1. Creation phase when the function is called, but before it executes any code inside.
   JS engine is in the compilation phase and it scans over the function to compile the code.

   • Create the Scope Chain.
   • Create variables, functions and arguments.
   • Determine the value of this.

2. Activation / Code Execution phase

   • Assign values, references to functions and interpret / execute code.

• http://davidshariff.com/blog/what-is-the-execution-context-in-javascript/
• https://hackernoon.com/execution-context-in-javascript-319dd72e8e2c
• http://speakingjs.com/es5/ch16.html - Environments: Managing Variables