JavaScript Advanced Programming Summary

Execution Environment and scope:

All global variables and functions are created as properties and methods of the Window object. When all the code in an execution environment finishes , the environment is destroyed, and all the variables and function definitions stored therein are destroyed (the global execution Environment is not destroyed until the application is retired- for example, when the Web page or browser is closed).

Each function has its own execution environment. When the execution flow enters a function, the environment of the function is pushed into an environment stack.
And after the function is executed, the stack pops its environment,

JavaScript Advanced Programming Summary