1 // Setup
 2 var collection = {
 3     "2548":{
 4         "album": "Slippery When Wet",
 5         "artist": "Bon Jovi",
 6         "tracks": [
 7              "Let It Rock",
 8              "You Give Love a Bad Name"  
 9         ]
10     },  
11     "2468":{
12         "album": "1999",
13         "artist": "Prince",
 
14         "tracks": [
15             "1999",
16             "Little Red Corvette"
17         ]
18     },  
19     "1245":{
20         "artist": "Robert Palmer",
21         "tracks": []
22     },
23     "5439":{
24         "album": "ABBA Gold"
25     }
26 };
27 
28 // Keep a copy of the collcection for tests
 

29 var collectionCopy = JSON.parse(JSON.stringify(collection));
30 
31 // update 
32 function updateRecords(id,prop,value){
33     if(value === ""){
34         // 如果值為空, 則刪除這個屬性
35         delete collection[id][prop];
36     }else if (prop === "tracks"){
37         collection[id][prop] = collection[id][prop] || []; 
 
38         // 如果 track 存在, 則不做變動; 若不存在, 則建立一個track, 並將[]賦給它
39         collection[id][prop].push(value); // 賦值 （新增至末端）   
40     } else{
41         collection[id][prop] = value;
42     }
43 
44     return collection;
45 }    
46 
47 // Alter values below to test your code
48 console.log(updateRecords(5439,"artist","ABBA")); 

LINK:https://www.youtube.com/watch?v=PkZNo7MFNFg&t=241s 2:03:00