The Scope Chain

the scope chain is the mechanism used by a javascript runtime that references a chain of parent scopes to resolve an identifier

when an identifier is referenced but not located in the "local scope", the scope chain traverses up to a parent scope until the identifier is found

  var peanuts = 'peanuts';

  function allergies() {

   return peanuts;

  }

  allergies();

Scope Chain Traversal

Nested Functions

   
    var newYorkBoroughs = ['Brooklyn', 'The Bronx', 'Manhattan', 'Queens', 'Staten Island'];
    
    function manhattan() {

        var manhattanLS = 'manhattan';
    
        function soHo() {
        
            var soHoLS = 'soHo';

            function chelsea() {

                var chelseaLS = 'chelsea';
                console.log(manhattan, soHoLS, chelseaLS, newYorkBoroughs);
            }

            chelsea();
        }
    
        soHo();
    }

    manhattan();

Scope Chain Traversal Example

Nested Functions

   
    var newYorkBoroughs = ['Brooklyn', 'The Bronx', 'Manhattan', 'Queens', 'Staten Island'];
    
    function manhattan() {

        var manhattanLS = 'manhattan';
    
        function soHo() {
        
            var soHoLS = 'soHo';
                        
        }
    
        soHo();
    }

    function chelsea() {

        var chelseaLS = 'chelsea';
        console.log(chelseaLS, newYorkBoroughs);
    }
    
    chelsea();

    manhattan();

Nested Functions

Reference Error

var newYorkBoroughs = ['Brooklyn', 'The Bronx', 'Manhattan', 'Queens', 'Staten Island'];

function manhattan() {
  var manhattanLS = 'manhattan';
  return brooklyn;
}

manhattan();