Classic examples of JavaScript closure

closures-example.js

function buildFunctions() {
  
  var arr = [];
  
  for(var i=0; i<3; i++) {
          
    // add three function to arr
    arr.push(
      function() {
        console.log(i);
      }
    )
    
  }  
  
  return arr;
}

var func_arr = buildFunctions();

func_arr[0](); // 3
func_arr[1](); // 3
func_arr[2](); // 3


function buildFunctions2() {
  
  var arr = [];
  
  for(var i=0; i<3; i++) {
    
    // add three function to arr, use iife to create 
    // three more execution context and store i's value
    arr.push(
      (function(j){
        return function() {
          console.log(j);
        }
      }(i))
    )
    
  }  
  
  return arr;
}


var func_arr2 = buildFunctions2();

func_arr2[0](); // 0
func_arr2[1](); // 1
func_arr2[2](); // 2