javascript - What is the difference and relationship between execution context and lexical environment?

Question

In JavaScript: Understanding the Weird Parts lexical environment is explained as the scope of your code while execution context is a collection of lexical environments, and that it includes stuff beyond your written code.

The descriptions of these terms still sound overlapping in functionality and it's unclear as to what execution context does or how it does it.

Answer 1

The best way to think of an execution context is as a stack frame, while lexical environments are indeed the scopes.

The respective spec chapters (§8.1 Lexical Environments and §8.3 Execution Contexts) explain:

• Execution contexts contain the current evaluation state of code, a reference to the code (function) itself, and possibly references to the current lexical environments.
  Execution contexts are managed in a stack.
• Lexical environments contain an environment record in which the variables are stored, and a reference to their parent environment (if any).
  Lexical environments build a tree structure.

With every change of the execution context, the lexical environment changes as well. However the lexical environment may change independently from that as well, for example when entering a block.