如何遍历对象，hasOwnProperty()方法，和 in 的区别【CordeWars实践】 Pete, the baker

1.如何遍历对象

for in

但是for in会返回继承的属性。如果只需要返回对象自身的属性，需要用hasOwnProperty()方法筛选

※更推荐使用Object.keys()

2.hasOwnProperty与in的区别

hasOwnProperty() 只能判断是否是属于自身的属性

in 可以找到原型上的属性

3.CodeWars实战：Pete, the baker

Pete likes to bake some cakes. He has some recipes and ingredients. Unfortunately he is not good in maths. Can you help him to find out, how many cakes he could bake considering his recipes?

Write a function cakes(), which takes the recipe (object) and the available ingredients (also an object) and returns the maximum number of cakes Pete can bake (integer). For simplicity there are no units for the amounts (e.g. 1 lb of flour or 200 g of sugar are simply 1 or 200). Ingredients that are not present in the objects, can be considered as 0.

Examples:

// must return 2
cakes({flour: 500, sugar: 200, eggs: 1}, {flour: 1200, sugar: 1200, eggs: 5, milk: 200}); 
// must return 0
cakes({apples: 3, flour: 300, sugar: 150, milk: 100, oil: 100}, {sugar: 500, flour: 2000, milk: 2000}); 

我的解答：

function cakes(recipe, mine) {
  var arr=[];
  for (var prop in recipe){
    if(recipe.hasOwnProperty(prop)){
      if(mine.hasOwnProperty(prop)){
        arr.push(Math.floor(mine[prop]/recipe[prop]));
      }
      else return 0;
    }
  }
  return Math.min(...arr);
}