Make a Person Using Getters and Setters: JavaScript not understanding where my codebase is performing the wrong action. Help requested - constructor

Question

The "Make a Person" intermediate algorithm scripting challenge on freeCodeCamp requires you to fill an object constructor with the following methods:
/*
getFirstName()
getLastName()
getFullName()
setFirstName(first)
setLastName(last)
setFullName(firstAndLast)
*/
My code is as follows and includes the test cases and their required values commented in at the end:
const Person = function(firstAndLast) {
// Only change code below this line
// Complete the method below and implement the others similarly
//create a holder variable to hold a copy of the full name passed as parameter
let fullName = firstAndLast;
//create a variable to pay respect to "DRY" so as not to have to type this variable and method multiple times throughout
let splitter = fullName.split(" ");
//return the first name from the full name passed as parameter
this.getFirstName = function() {
return splitter[0];
};
//return the last name from the full name passed as parameter
this.getLastName = function() {
return splitter[1];
};
//return the full name passed as a parameter
this.getFullName = function() {
return fullName;
};
//update the full name to now include the given first name instead of the original passed parameter
this.setFirstName = function(first) {
fullName = first + " " + splitter[1];
};
//update the full name to now include the given last name instead of the original passed parameter
this.setLastName = function(last) {
fullName = splitter[0] + " " + last;
};
//update the full name to the given firstAndLast name instead of the original passed parameter
this.setFullName = function(newFull) {
fullName = newFull;
};
};
//create a new Person, bob, and name him 'Bob Ross'
const bob = new Person('Bob Ross');
//expected to return => 'Bob Ross'
let result = bob.getFullName();
//no expected return value, but fullName should now return => 'Haskell Curry'
bob.setFullName('Haskell Curry')
//my code here returns => 'Haskell Curry'
let result2 = bob.getFullName();
//my code here returns => 'Bob'
//should be returning => 'Haskell'
let result3 = bob.getFirstName();
//my code here returns => 'Ross'
//should be returning => 'Curry'
let result4 = bob.getLastName();
//Console.log in place for value testing during algorithm creation
console.log(result, result2, result3, result4)
//Check for length of bob, should not exceed 6 for the purposes of this test
console.log(Object.keys(bob).length)
/*Tests
Required returning values for each test
bob instanceof Person => true (Passing)
Object.keys(bob).length => 6 (Passing)
bob.firstName => undefined (Passing)
bob.lastName => undefined (Passing)
bob.getFirstName() => "Bob" (Passing)
bob.getLastName() => "Ross" (Passing)
bob.getFullName() => "Bob Ross" (Passing)
bob.getFullName() => "Haskell Ross" AFTER bob.setFirstName("Haskell") (Passing)
bob.getFullName() => "Haskell Curry" AFTER bob.setLastName("Curry") (Passing)
bob.getFullName() => "Haskell Curry" AFTER bob.setFullName("Haskell Curry") (Passing)
bob.getFirstName() => "Haskell" AFTER bob.setFullName("Haskell Curry") (NOT Passing)
bob.getLastName() => "Curry" AFTER bob.setFullName("Haskell Curry") (NOT Passing)
*/
After checking my code up against the solution code, the two are virtually the same, the only differences are the usage of
let splitter = fullName.split(" ")
//this does not exist in the solution code
//used in my code to avoid having to type fullName.split(" ") multiple times throughout
And where the setters ask for parameters "first", "last", and "newFull", respectively, the solution code uses "name" for each instead
I couldn't imagine that these two differences could make that big of a difference, so could I get some clarity in the understanding of their importance, and furthermore, why my code won't pass all the cases as is? Thanks in advance!