javascript - Variable Environment vs lexical environment

Question

I need to understand the difference between Variable Environment vs lexical environment in JavaScript. Actually I go through some notes available in stackoverflow and the doc but they are very hard to understand.I would be happy if you can explain it to me simply due my bad English knowledge

Answer 1

Note

This answer relates to ECMA-262 ed 5.1. Later editions have modified the description of variable and lexical environments to accommodate lexical scoping of let and const (which are both block scoped).

According to ECMA-262 §10.3, variable environment is a certain type of lexical environment. Both are "specification types" that are used solely to describe features of ECMAScript. You can't access them or modify them directly in anyway, and ECMAScript implementations don't have to implement them in any specific way, they just have to behave as if they were implemented per the specification.

A lexical environment consists of an environment record, which can be thought of as an object whose properties are the variable and function names declared within the associated execution context. It also has, for functions, identifiers from the formal parameter list in the function declaration or expression (e.g. function foo(a, b){} effectively declares a and b as variables on foo's environment record).

A lexical environment also has a link to any outer lexical environment (i.e. its scope chain), so it is used to resolve identifiers outside the current an execution context (e.g. global variables from within a function). They can be associated with other structures besides functions and execution contexts, e.g. try..catch and with statements.

A variable environment is just the part of a lexical environment within the execution context, essentially just the variables and functions declared within the current context.

Anyone who wants to correct the above, please chime in.