在freecodecamp遇到的题(一)

 1.函数 lookUp 有两个预定义参数：firstName值和prop属性 。

函数将会检查通讯录是否存在一个联系人的firstName属性等于firstName值，还会检查对应联系人是否存在 prop属性。

如果它们都存在，函数返回prop属性对应的值。

如果firstName 值不存在，返回 "No such contact"。

如果prop 属性不存在，返回 "No such property"。

//Setup
var contacts = [
    {
        "firstName": "Akira",
        "lastName": "Laine",
        "number": "0543236543",
        "likes": ["Pizza", "Coding", "Brownie Points"]
    },
    {
        "firstName": "Harry",
        "lastName": "Potter",
        "number": "0994372684",
        "likes": ["Hogwarts", "Magic", "Hagrid"]
    },
    {
        "firstName": "Sherlock",
        "lastName": "Holmes",
        "number": "0487345643",
        "likes": ["Intriguing Cases", "Violin"]
    },
    {
        "firstName": "Kristian",
        "lastName": "Vos",
        "number": "unknown",
        "likes": ["Javascript", "Gaming", "Foxes"]
    }
];

function lookUp(firstName, prop){
// Only change code below this line
  var _firstname = false,_prop = false;
  for(var i = 0; i < contacts.length; i++){
    if(firstName == contacts[i].firstName && contacts[i][prop]){
      return contacts[i][prop];
    }
    if(contacts[i].firstName == firstName){
      _firstname = true;
      if(contacts[i][prop]){
        _prop = true;
      }
    }
  }
  if(!_firstname){return "No such contact";}
  if(!_prop){return "No such property";}
  // Only change code above this line
}
// Change these values to test your function
lookUp("Kristian", "lastName");

2.将给定的数字转换成罗马数字。

function convert(num) {
  var romanArr = ["I","V","X","L","C","D","M"];
  //               1   5  10  50  100 500 1000
  var str = "",index = 0;
  while(num > 0){
    var roman = num % 10;
    switch(roman){
      case 3:
        str = romanArr[index] + str;
        roman --;
      case 2:
        str = romanArr[index] + str;
        roman --;
        //continue;
      case 1:
        str = romanArr[index] + str;
        break;  
      case 4:
        str = romanArr[index] + str;
        str = romanArr[index + 1] + str;
        break;
      case 8:
        str = romanArr[index] + str;
        roman --;
      case 7:
        str = romanArr[index] + str;
        roman --;
      case 6:
        str = romanArr[index] + str;
        roman --;
        //continue;
       case 5:
        str = romanArr[index + 1] + str;
        break; 
      case 9:
        str = romanArr[index] + str;
        str = romanArr[index + 2] + str;
        break;
      default:
        break;

    }
    index += 2;
    num = Math.floor(num / 10);
  }
  return str;
 //return num;
}

convert(4);

3.

写一个 function，它遍历一个对象数组（第一个参数）并返回一个包含相匹配的属性-值对（第二个参数）的所有对象的数组。如果返回的数组中包含 source 对象的属性-值对，那么此对象的每一个属性-值对都必须存在于 collection 的对象中。

例如，如果第一个参数是 [{ first: "Romeo", last: "Montague" }, { first: "Mercutio", last: null }, { first: "Tybalt", last: "Capulet" }]，第二个参数是 { last: "Capulet" }，那么你必须从数组（第一个参数）返回其中的第三个对象，因为它包含了作为第二个参数传递的属性-值对。

function where(collection, source) {
  var arr = [];
  // What's in a name?
  var pro = Object.keys(source);
  //遍历colletion
  for(var j = 0;j < collection.length; j++){
    //遍历source里面的对象
    var boo = true;
    for(var i in source){
      if(source[i] != collection[j][i] || !collection[j].hasOwnProperty(i)){
        boo = false;
      }
    }
    /*for(var i = 0;i < pro.length;i++){
      if(!collection[j].hasOwnProperty(pro[i]) || collection[j][pro[i]] != source[pro[i]]){
        boo = false;
      }
    }*/
    if(boo){
      arr.push(collection[j]);
    }
  }
  return arr;
}

where([{ "a": 1, "b": 2 }, { "a": 1 }, { "a": 1, "b": 2, "c": 2 }], { "a": 1, "b": 2 });

老版本浏览器不支持for in,所以项目中尽量不要使用