What is a 'Closure'?

Question

I asked a question about Currying and closures were mentioned. What is a closure? How does it relate to currying?

Answer 1

If you are from the Java world, you can compare a closure with a member function of a class. Look at this example

var f=function(){
  var a=7;
  var g=function(){
    return a;
  }
  return g;
}

The function g is a closure: g closes a in. So g can be compared with a member function, a can be compared with a class field, and the function f with a class.