notes

Scope

Compilation

1. JavaScript is a compiled language. The difference between it and C++ that in C++ compilation happens in a build step ahead of time, in JavaScript compilation that occurs happends microseconds before the code is executed.
2. Compilation have the following steps:
   • Tokenizing - breaking up a string of characters into meaningful chunks, called tokens. For instance, consider the program var a = 2;. This program would likely be broken into the following tokens: var, a, =, 2 and ;.
   • Parsing - taking a stream (array) of tokens and turning it into a tree of nested elements “AST” (Abstract Syntax Tree).
     The tree for var a = 2;:
     • Variable Declaration
       • Identifier (whose value is a)
       • AssignmentExpression
         • NumbericLiteral (whose value is 2)
   • Code-Generating - the process of taking an AST and turning it into executable code.

Code execution

1. Engine - responsible for start-to-finish compilation
2. Compiler - handles all the dirty work of parsing and code-generation
3. Scope - collects and maintains a look-up list of all declared identifiers (variables), and enforces a strict set of rules as how these are accessible to currently executin code.