var AddStrategy = function(){
  this.caculate = function(num1, num2){
    return num1 + num2;
  }
}
 
var SubStrategy = function(){
  this.caculate = function(num1, num2){
    return num1 - num2;
  }
}
 
var MulStrategy = function(){
  this.caculate = function(num1, num2){
    return num1 * num2;
  }
}
 
var DivStrategy = function(){
  this.caculate = function(num1, num2){
    return num1 / num2;
  }
}
 
var Context = function(strategy){
  var _strategy = strategy;
 
  this.executeStrategy = function(num1, num2){
    return _strategy.caculate(num1, num2)
  }
}
var add = new Context(new AddStrategy());
var sub = new Context(new SubStrategy());
var mul = new Context(new MulStrategy());
var div = new Context(new DivStrategy());
 
console.log('1 + 2 = ' + add.executeStrategy(1, 2));
console.log('5 - 1 = ' + sub.executeStrategy(5, 1));
console.log('3 * 2 = ' + mul.executeStrategy(3, 2));
console.log('8 / 2 = ' + div.executeStrategy(8, 2));
 
// 1 + 2 = 3
// 5 - 1 = 4
// 3 * 2 = 6
// 8 / 2 = 4