Why explicit shadowing is important. Many people wrongfully claim that the same problem arises with defines in Scheme. It doesn't.

cs-scope.coffee

$('.test').each (i, e) ->
  e = $(e)
  content = e.find('.content') # Gee, I hope it's not global!
  
  e.find('.refresh').on 'click', (e) ->
    $.ajax {
      method: 'GET',
      url: 'http://example.com',
      type: 'text'
      success: (res) -> content.html(res)
    }

js-scope.js

var x = 5;
function f(y) {
  var x = 10; // not the same variable as x in the outer scope
  return x + y;
}

console.log(f(10)); // 20
console.log(x); // 5

scm-scope.scm

#lang r5rs

(define x 5)
(define (f y)
  (define x 10)
  (+ x y))

(display (f 10)) ; => 20
(newline)
(display x) ; => 5