DeepJavaScriptFoundations

Notes on Kyle Simpson's course Deep JavaScript Foundations on Frontend Masters

Scope: Set of rules for storing variables in some location and for finding those variables at a later time. Where to look for things.

JavaScript is a compiled language. It's a common misconseption that it's an interpreted language.
A good question to ask when thinking about scope is, Who is doing the looking?
Scope is a compiled time process. It's at compile time that all scope decisions are made.
JavaScript makes two passes before actually executing.
On the first pass, compilation, the lexical scope is set up.
First pass when compiling look for all variable declarations and all the scopes they get added to.
The compiler and scope manager have a conversations.
The individual unit of scope is the function.
As the JavaScript compiler enters a function, it will begin looking for declaration(s) inside that scope and recursively process them.
- Once all scopes have been compiled, the execution phase can begin.
As the execution phase continues within the function scope, the same Left-Hand Side (LHS) and Right-Hand Side (RHS) operations are applied.
- Things get a little interesting with undeclared variables. They are automatically declared in the global scope.
- LHS is the target of an assignment.
- RHS is the source of an assignment.

Scope Manager && Compiler Dialogue

var foo = "bar";

function bar() {
  var foo = "baz";
}

function baz(foo) {
  foo = "bam";
  baz = "yay";
}

smeads/DeepJavaScriptFoundations