What is the execution context and what happens in its two phases?

An execution context is the environment in which JavaScript code is evaluated. The engine maintains a stack of contexts (the call stack); each function invocation pushes a new one.

Each context contains:

• Variable environment — var, function declarations, let/const bindings
• this binding
• Outer reference — link to the lexical (parent) environment for scope chain lookups

Two phases

1. Creation phase

   • Create the variable object / lexical environment.
   • Set up scope chain (reference to outer environment).
   • Determine this (global, function, or new binding).
   • Hoist function declarations and var (initialized to undefined).
   • Register let/const in TDZ (not initialized yet).

2. Execution phase

   • Run code line by line.
   • Assign values, evaluate expressions, invoke functions.

console.log(typeof foo) // "function" — hoisted declaration
console.log(bar)        // undefined — hoisted var

function foo() {}
var bar = 1

When a function returns, its execution context is popped from the stack and eligible for garbage collection (unless closures retain references).

Understanding execution context ties together hoisting, scope, closures, and the call stack.