[Intermediate Algorithm] - Everything Be True

題目

全部的東西都是真的！

完善編輯器中的every函數，若是集合(collection)中的全部對象都存在對應的屬性(pre)，而且屬性(pre)對應的值爲真。函數返回ture。反之，返回false。

記住：你只能經過中括號來訪問對象的變量屬性(pre)。

提示

提示：你能夠有多種實現方式，最簡潔的方式莫過於Array.prototype.every()。

測試用例

• every([{"user": "Tinky-Winky", "sex": "male"}, {"user": "Dipsy", "sex": "male"}, {"user": "Laa-Laa", "sex": "female"}, {"user": "Po", "sex": "female"}], "sex") 應該返回 true。
• every([{"user": "Tinky-Winky", "sex": "male"}, {"user": "Dipsy"}, {"user": "Laa-Laa", "sex": "female"}, {"user": "Po", "sex": "female"}], "sex")應該返回 false。
• every([{"user": "Tinky-Winky", "sex": "male", "age": 0}, {"user": "Dipsy", "sex": "male", "age": 3}, {"user": "Laa-Laa", "sex": "female", "age": 5}, {"user": "Po", "sex": "female", "age": 4}], "age") 應該返回 false。
• every([{"name": "Pete", "onBoat": true}, {"name": "Repeat", "onBoat": true}, {"name": "FastFoward", "onBoat": null}], "onBoat") 應該返回 false
• every([{"name": "Pete", "onBoat": true}, {"name": "Repeat", "onBoat": true, "alias": "Repete"}, {"name": "FastFoward", "onBoat": true}], "onBoat") 應該返回 true
• every([{"single": "yes"}], "single") 應該返回 true
• every([{"single": ""}, {"single": "double"}], "single") 應該返回 false
• every([{"single": "double"}, {"single": undefined}], "single")應該返回 false
• every([{"single": "double"}, {"single": NaN}], "single") 應該返回 false

分析思路

1. 判斷是否對象包含屬性，使用 Object.hasOwnProperty();
2. 判斷屬性的值是否爲真，直接使用 Object[pro] 便可；

代碼

function every(collection, pre) {
  // Is everyone being true?
  return collection.every(function(element, index, array) {
    return (element.hasOwnProperty(pre) && element[pre]);
  });
}

every([{"user": "Tinky-Winky", "sex": "male"}, {"user": "Dipsy", "sex": "male"}, {"user": "Laa-Laa", "sex": "female"}, {"user": "Po", "sex": "female"}], "sex");