What is the scope chain in JavaScript?

Every function and block creates a scope. When code reads a variable, the engine looks in the current scope first, then walks outward through the chain of enclosing scopes until it finds the binding or reaches the global scope. That lookup path is fixed when the code is written, not when it is called.

const appName = "VocalHyre";

function outer() {
  const topic = "closures";

  function inner() {
    const detail = "lexical";
    console.log(appName, topic, detail);
  }

  inner();
  console.log(detail); // ReferenceError
}

outer();

Lexical, not dynamic

Lexical scoping means the call site does not decide which variables are visible. A function called from another file still sees the scope where it was defined. That is also why closures can keep private state alive after the outer function returns.

The scopes you will meet

• Global or module scope: top-level bindings
• Function scope: parameters and var declarations
• Block scope: let, const, class and function declarations inside a block
• Catch scope: the error binding in catch (error)

Shadowing happens when an inner declaration uses the same name as an outer one. The inner binding wins for the rest of that block, but the outer binding is unchanged.

let count = 1;

function increment() {
  let count = 2;
  count += 1;
  return count;
}

console.log(increment()); // 3
console.log(count); // 1