Original JavaScript

[1] In this book, we do not show the interpreter's response to evaluating definitions, since this is highly implementation-dependent. In this book, we do not show the interpreter's response to evaluating programs that end with declarations, since this might depend on previous statements. See exercise 4.13 for details.
[2] Chapter 3 will show that this notion of environment is crucial for understanding how the interpreter works. Chapter 4 will use environments for implementing interpreters.
1.1.2  Naming and the Environment