Basic Javascript: Record Collection - Push Nested Object

JavaScript
1

What is the difference between normal assigning vs pushing? With respect to the question which wants to keep the newly inserted element at the last.

Question link: https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/basic-javascript/record-collection

Please see the cases below case 1 and case 2 in the 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"
  }
};

// Only change code below this line
function updateRecords(id, prop, value) {

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

//at this point tracks property is empty after previous line so why necessary to push?            
          collection[id][prop].push(value);          //case 1 using push
         // collection[id][prop]=value;				//case 2 without using push
            
           console.log('Inside tracks '+collection[id][prop]);
        }
        else
        {
            console.log("Prop is present with elements in it");
            
        	collection[id][prop].push(value);
        }
    }
        
    else if(prop=="album")
    {
        collection[id][prop]=value;
    }        
        
        }
           else
   {
    delete collection[id][prop];   
   }
   console.log('End Console '+ collection[id][prop])
   console.log("_________")
  //return collection;
}

updateRecords(5439, "artist", "ABBA");
updateRecords(5439, "tracks", "Take a Chance on Me")
updateRecords(2548, "tracks", "")
updateRecords(2468, "tracks", "Free")
3

** I have used this to assign an empty array to “tracks” property**

collection[id][prop]=[];

Now at this point tracks property is an empty array so why necessary to push?
why can we not use this directly?

 collection[id][prop]=value;
5

thanks! @camperextraordinaire