方法一：

//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 hasName=false;
  var hasProp=false;
  for(var i in contacts){
    if(firstName == contacts[i].firstName){
      hasName=true;
      if(contacts[i].hasOwnProperty(prop)){
        console.log("_s");
        return contacts[i][prop];
      }
      else{continue;}
    }else{continue;}
  }
  if(!hasName){
    return "No such contact";
  }
  if(!hasProp){
    return "No such property";
  }
// Only change code above this line
}
// Change these values to test your function
lookUp("Akira", "likes");

方法二：

//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
for(var i=0;i<contacts.length;i++){
  if(contacts[i].firstName===firstName)
     return contacts[i][prop]=== undefined ?  "No such property" :contacts[i][prop];
}
    return "No such contact";
// Only change code above this line
}
// Change these values to test your function
lookUp("Akira", "likes");

方法三：

//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
for(i=0;i<contacts.length;i++){
  if(contacts[i].firstName==firstName){
    if(contacts[i].hasOwnProperty(prop)){
      return contacts[i][prop];
    }
    else return "No such property";
  }
}
  return "No such contact";
// Only change code above this line
}
// Change these values to test your function
lookUp("Akira", "likes");