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Javascript: Closure and Lexical Scope

The two are separate topics, I just happen to put them in the same post for now.


Closure

Closure is the capability to remember it's lexical scope, even when executed outside it's lexical scope.
If two inner functions, are within the same scope, they share the same closure.    


Lexical scope

The lexical scope is the scope in which a variable is declared during the first pass of the javascript compilation, which has two passes, compilation and execution.

During the compilation pass, the compiler goes through the code looking for formal declaration, that is, var, function and parameters of function.

For each of these formal declarations, the compiler will check the current lexical scope, and add this identifier if it isn't already there.

Then at the second pass, execution, the compiler will run the code as we are intuitively use to and once it reaches the the identifiers found earlier, will ask if they are left hand side(RHS), or right hand side (LHS).

If the LHS is known in the current scope, it will assign as expected, if not it will go up a level in scope to assign it, all the way up to the global scope, and will throw an exception if it has not been found(in strict mode), or declare the identifier(in loose mode).

If the identifier is a RHS, the compiler will keep asking the scope manager the same way it did with the LHS, and if it reaches the global scope without finding a declaration, it will throw a reference exception in both strict and loose mode.

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