Record Collection - Problem Solving

JavaScript
1

Tell us what’s happening:

Can someone explain to me how you would know that this was the solution? And what does the second if conditional mean.

Thanks

Your code so far


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

  return collection;
}
   



  
 




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

Your browser information:

2

.
GIVEN the collection object as shown, and
GIVEN you have three variables id, prop and value that are the arguments to the function, and
GIVEN you can do lookups on the object by doing collection[id].prop,
THEN

If prop isn’t “tracks” and value isn’t empty (“”), update or set the value for that record album’s property.

IF prop is not "tracks" AND value is not "" THEN
  SET collection[id].prop TO value
ENDIF

If prop is “tracks” but the album doesn’t have a “tracks” property, create an empty array before adding the new value to the album’s corresponding property.

If prop is “tracks” and value isn’t empty (“”), push the value onto the end of the album’s existing tracks array

IF prop is "tracks" AND the collection does not have a property "tracks" THEN
  SET collection[id].tracks to []
  PUSH value TO collection[id].tracks
ENDIF

IF prop is "tracks" AND the collection has a property "tracks" THEN
  PUSH value TO collection[id].tracks
ENDIF

If value is empty (“”), delete the given prop property from the album.

IF value is "" THEN
  DELETE collection[id].prop
ENDIF

Then

RETURN collection

So, translating that pseudocode to JS:

function updateRecords(id, prop, value) {
  if (prop !== "tracks" && value !== "") {
    collection[id].prop = value;
  } else if (prop === "tracks" && collection.hasOwnProperty("tracks") === false) {
    collection[id].prop = [];
    collection[id].prop.push(value);
  } else if (prop === "tracks" && collection.hasOwnProperty("tracks") === true) {
    collection[id].prop.push(value);
  } else if (value === "") {
    delete collection[id].prop;
  }
  return collection;
}

That is just the instructions, in the order they were written, translated to JavaScript.

There is a flaw in the logic, which is important. If value is “”, then the property gets deleted, but if prop is “tracks”, I don’t check that, so the function could fail to work: the tracks logic will happen before I get a chance to delete. So then I need to change the order (putting that condition first should cause all the tests to pass), or nest the if statements. There is also duplication, (which is not hugely important) but can be cleaned up. And you get to something close to that solution you posted

Edit: also, I used a function that JS provides called hasOwnProperty. This returns true or false if an object has the property you pass to the function or not. There’s a hint for what to Google for in the description anyway:

…but the album doesn’t have a “tracks” property,

& you could Google “check if a javascript object has a property” and most of the results would mention hasOwnProperty

If you mean this:

if (collection[id][prop])

So anything in those brackets in an if statement JS will convert to either true or false. And if the prop is not in the collection, it’s value will be undefined. And when JS convert that, it converts to false. Otherwise it will be true, and the code inside that block will run.

Note this is not a great way to check things: it’s very easy to accidentally convert a value to false when you just wanted to check it was true and vice versa IMO always try to do something in the if statement that you know always either returns true or false (like using === or > or < or whatever).

1 Like
3

Excellent Dan! Thanks!