What Is a 'Closure'?

Variable scope

When you declare a local variable, that variable has a scope. Generally, local variables exist only within the block or function in which you declare them.

function() {
  var a = 1;
  console.log(a); // works
}    
console.log(a); // fails

If I try to access a local variable, most languages will look for it in the current scope, then up through the parent scopes until they reach the root scope.

var a = 1;
function() {
  console.log(a); // works
}    
console.log(a); // works

When a block or function is done with, its local variables are no longer needed and are usually blown out of memory.

This is how we normally expect things to work.