Closure

closure.js

var addTo = function(passed){
	var inner=2;
  return passed+inner;
};

console.log(addTo(3)); // 5

// Constant arguments can also be declared outside the function, and are accessible inside
var passedArg=3;
var addToNoArgs = function(){
	var innerVal=2;
  return innerVal+passedArg;
}
console.log(addToNoArgs()); // We get the same answer 5

/*
  This is possible due to lexical scoping used by Js. This concept of functions being able to accesss/ store values from outer arguments
  is called closure. Although it can get more complex, this example serves as a basic understanding
*/

console.dir(addToNoArgs);

// Lets take a more complex example
var addNum = function(passedArg){
	var add= function(inner){
  	return inner+passedArg;
  };
  return add;
};

var add3 = addNum(3);
var add4 = addNum(4);
console.log(add3(1)); // prints 4
console.log(add4(1)); // prints 5
// Hence by using closures, addNum preserves the value passed to it, and uses it in the computation of the add method!

// Currying is also a possible extension of Closures

var add= function(a){
	return function(b){
  	return a+b;
  }
};

var addToFive = add(5);
console.log(addToFive(1)); // returns 6