Basic JavaScript: Record Collection. I have a problem

sp2012 · June 26, 2019, 7:51am

Hello,

I have this code:

// Setup
var collection = {
    "2548": {
      "album": "Slippery When Wet",
      "artist": "Bon Jovi",
      "tracks": [ 
        "Let It Rock", 
        "You Give Love a Bad Name" 
      ]
    },
    "2468": {
      "album": "1999",
      "artist": "Prince",
      "tracks": [ 
        "1999", 
        "Little Red Corvette" 
      ]
    },
    "1245": {
      "artist": "Robert Palmer",
      "tracks": [ ]
    },
    "5439": {
      "album": "ABBA Gold"
    }
};
// Keep a copy of the collection for tests
var collectionCopy = JSON.parse(JSON.stringify(collection));

// Only change code below this line
function updateRecords(id, prop, value) {
  if(prop !== "tracks" && value !== "") {

    collection[prop].push(value);
  }
  
  if(prop === "tracks" && collection.hasOwnProperty("tracks") === false) {

    collection.tracks = [];
    collection.tracks.push(value);
  }

   if(prop === "tracks" && value !== "") {
     collection.tracks.push(value);
   }

   if(value === ""){
     delete collection[prop];
   }

  return collection;
}

// Alter values below to test your code
updateRecords(5439, "artist", "ABBA");

I am getting error: Cannot read property ‘push’ of undefined

Any ideas?

JamesRea83 · June 26, 2019, 8:26am

Here on line 35-

You’re trying to access the property “artist” of the object collection. That property doesn’t exist. You need to first make use of the id argument you’re passing in to the updateRecords function.

sp2012 · June 26, 2019, 11:00am

Thanks. How do I make use of the id argument?

JamesRea83 · June 26, 2019, 3:07pm

You can chain together property accessors to go through the different levels in nested objects. In this case-

collection[id][prop]

will get you the array you are looking to push to.

sp2012 · June 26, 2019, 3:14pm

Thanks.

OK, so now I have this code:

// Setup
var collection = {
    "2548": {
      "album": "Slippery When Wet",
      "artist": "Bon Jovi",
      "tracks": [ 
        "Let It Rock", 
        "You Give Love a Bad Name" 
      ]
    },
    "2468": {
      "album": "1999",
      "artist": "Prince",
      "tracks": [ 
        "1999", 
        "Little Red Corvette" 
      ]
    },
    "1245": {
      "artist": "Robert Palmer",
      "tracks": [ ]
    },
    "5439": {
      "album": "ABBA Gold"
    }
};
// Keep a copy of the collection for tests
var collectionCopy = JSON.parse(JSON.stringify(collection));

// Only change code below this line
function updateRecords(id, prop, value) {
  if(prop !== "tracks" && value !== "") {

    collection[id][prop].push(value);
  }
  
  if(prop === "tracks" && collection.hasOwnProperty("tracks") === false) {

    collection.id.tracks = [];
    collection.id.tracks.push(value);
  }

   if(prop === "tracks" && value !== "") {
     collection.id.tracks.push(value);
   }

   if(value === ""){
     delete collection[id][prop];
   }

  return collection;
}

// Alter values below to test your code
updateRecords(5439, "artist", "ABBA");

but I still get error: Cannot read property ‘push’ of undefined

JamesRea83 · June 26, 2019, 3:21pm

Ah I see.

push() is used to add a value to an existing array. That’s not what you’re trying to do in this instance.

With updateRecords(5439, "artist", "ABBA"), you’re trying to add a new key value pair to the object “5439”.

Instead of using push(), you need to use an assignment operator =.

sp2012 · June 26, 2019, 4:19pm

Thanks, I see.

Here is my code now:

// Setup
var collection = {
    "2548": {
      "album": "Slippery When Wet",
      "artist": "Bon Jovi",
      "tracks": [ 
        "Let It Rock", 
        "You Give Love a Bad Name" 
      ]
    },
    "2468": {
      "album": "1999",
      "artist": "Prince",
      "tracks": [ 
        "1999", 
        "Little Red Corvette" 
      ]
    },
    "1245": {
      "artist": "Robert Palmer",
      "tracks": [ ]
    },
    "5439": {
      "album": "ABBA Gold"
    }
};
// Keep a copy of the collection for tests
var collectionCopy = JSON.parse(JSON.stringify(collection));

// Only change code below this line
function updateRecords(id, prop, value) {
  if(prop !== "tracks" && value !== "") {

    collection[id][prop] = value;
  }
  
  if(prop === "tracks" && collection.hasOwnProperty("tracks") === false) {

    collection.id.tracks = [];
    collection.id.tracks.push(value);
  }

   if(prop === "tracks" && value !== "") {
     collection.id.tracks.push(value);
   }

   if(value === ""){
     delete collection[id][prop];
   }

  return collection;
}

// Alter values below to test your code
updateRecords(5439, "artist", "ABBA");

I get error: Cannot set property ‘tracks’ of undefined

sp2012 · June 26, 2019, 4:57pm

Thanks.

Here is my code now:

// Setup
var collection = {
    "2548": {
      "album": "Slippery When Wet",
      "artist": "Bon Jovi",
      "tracks": [ 
        "Let It Rock", 
        "You Give Love a Bad Name" 
      ]
    },
    "2468": {
      "album": "1999",
      "artist": "Prince",
      "tracks": [ 
        "1999", 
        "Little Red Corvette" 
      ]
    },
    "1245": {
      "artist": "Robert Palmer",
      "tracks": [ ]
    },
    "5439": {
      "album": "ABBA Gold"
    }
};
// Keep a copy of the collection for tests
var collectionCopy = JSON.parse(JSON.stringify(collection));

// Only change code below this line
function updateRecords(id, prop, value) {
  if(prop !== "tracks" && value !== "") {

    collection[id][prop] = value;
  }
  
  else if(prop === "tracks" && collection.hasOwnProperty("tracks") === false) {

    collection[id].tracks = [];
    collection.id.tracks.push(value);
  }

   else if(prop === "tracks" && value !== "") {
     collection[id].tracks.push(value);
   }

   else if(value === ""){
     delete collection[id][prop];
   }

  return collection;
}

// Alter values below to test your code
updateRecords(5439, "artist", "ABBA");

I get error: Cannot read property ‘tracks’ of undefined

sp2012 · June 27, 2019, 9:13am

Thanks.

Here is my code now:

// Setup
var collection = {
    "2548": {
      "album": "Slippery When Wet",
      "artist": "Bon Jovi",
      "tracks": [ 
        "Let It Rock", 
        "You Give Love a Bad Name" 
      ]
    },
    "2468": {
      "album": "1999",
      "artist": "Prince",
      "tracks": [ 
        "1999", 
        "Little Red Corvette" 
      ]
    },
    "1245": {
      "artist": "Robert Palmer",
      "tracks": [ ]
    },
    "5439": {
      "album": "ABBA Gold"
    }
};
// Keep a copy of the collection for tests
var collectionCopy = JSON.parse(JSON.stringify(collection));

// Only change code below this line
function updateRecords(id, prop, value) {
  if(prop !== "tracks" && value !== "") {

    collection[id][prop] = value;
  }
  
  else if(prop === "tracks" && collection.hasOwnProperty("tracks") === false) {

    collection[id].tracks = [];
    collection[id].tracks.push(value);
  }

   else if(prop === "tracks" && value !== "") {
     collection[id].tracks.push(value);
   }

   else if(value === ""){
     delete collection[id][prop];
   }

  return collection;
}

// Alter values below to test your code
updateRecords(5439, "artist", "ABBA");

I get errors:

After updateRecords(2468, “tracks”, “Free”), tracks should have “1999” as the first element.

After updateRecords(2548, “tracks”, “”), tracks should not be set

ilenia · June 27, 2019, 9:28am

this will always be false

sp2012 · June 27, 2019, 9:53am

Thanks. Why? And, how do I fix that?

ilenia · June 27, 2019, 10:49am

heck carefully what you have written. Does collection have a tracks property?

sp2012 · June 27, 2019, 11:50am

It has a tracks property. Only the last object lacks a tracks property.

ilenia · June 27, 2019, 12:03pm

are you really sure that collection has a tracks property?

so, if you do collection.tracks you should get something.

sp2012 · June 27, 2019, 12:41pm

I don’t get it, can you please explain? Tracks is in collection[id].tracks.

sp2012 · June 27, 2019, 1:40pm

I turned this:

into this: if( collection[id].hasOwnProperty(“tracks”) === false

and now it works.