[Intermediate Algorithm] - Everything Be True

题目

所有的东西都是真的！

完善编辑器中的every函数，如果集合(collection)中的所有对象都存在对应的属性(pre)，并且属性(pre)对应的值为真。函数返回ture。反之，返回false。

记住：你只能通过中括号来访问对象的变量属性(pre)。

提示

提示：你可以有多种实现方式，最简洁的方式莫过于Array.prototype.every()。

测试用例

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

分析思路

1. 判断是否对象包含属性，使用 Object.hasOwnProperty();
2. 判断属性的值是否为真，直接使用 Object[pro] 即可；

代码

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");