Define custom parameters inside javascript compare functions in JavaScript?

Question

I have an array of objects that needs sorting by last name, however the object only has firstname and fullname parameters, so for last name I have to use fullname.replace((firstname + " "), ""). Example array below.

const names = [
        {
            firstname: "John",
            fullname: "John Doe"
        },
        {
            firstname: "Amber",
            fullname: "Amber Smith"
        },
        {
            firstname: "Michael",
            fullname: "Michael Smith"
        },
        {
            firstname: "Jessica",
            fullname: "Jessica Kelly Charles"
        }
    ]

While I can use the "replace" every time inside a sort compare function, I'd much rather have something like this:

names.sort(function(a, b) {
            const lastname = fullname.replace((firstname+ " "), "");
            if (a.lastname < b.lastname) {
                return -1;
            } else if (a.lastname > b.lastname) {
                return 1;
            }
            return 0;
        });

Obviously lastname comes up as undefined. This has been rather hard to google for, and I think I'm missing some JavaScript basics here, but would greatly apprecite your help in helping me learn to write better code.

I can't unfortunately, just ammending something for work so needs to work as is! — fokicheva
– fokicheva, Commented Jan 18, 2022 at 15:11
There is no good way to extract a surname from a full name. It will either break when a middle name is included, or when the last name is multiple words, or break when the natural language of the name puts the surname first. That's why it's important to store the surname separately when the user inputs it. — James
– James, Commented Jan 18, 2022 at 20:31
@James absolutely true, unfortunately I'm not that one that has control over how these things are structured, so I have to make do with the assumption that lastname = fullname - firstname for now. I do agree though, storing first + last name separately would probably be a better practice! — fokicheva
– fokicheva, Commented Jan 19, 2022 at 13:37

T.J. Crowder · Accepted Answer · 2022-01-18 14:27:22Z

2

Your best bet is to modify the source of the array so it stores lastname upon collection.

If you can't do that:

Unless you do a prep pass through your array adding a lastname property, you'll have to compute it each and every time your sort callback is called, for both a and b.

names.sort((a, b) => {
    const alast = a.fullname.replace(a.firstname + " "), "");
    const blast = b.fullname.replace(b.firstname + " "), "");
    return alast.localeCompare(blast);
});

(Note I used localeCompare, which is always a better choice for names and other natural language strings than < and >. For instance, ask the French whether ç should really come after z as it does with < and >. ;-) )

That will recompute the lastname for the same object repeatedly, though, since the same object may be passed to sort (as either a or b) repeatedly. If you think that may be a problem, you could do that prep pass I mentioned:

// Build a map of entry to last names
const lastnames = new Map(names.map(entry => {
    const lastname = entry.fullname.replace(entry.firstname + " ", "");
    return [entry, lastname];
}));
// sort
names.sort((a, b) => {
    return lastnames.get(a).localeCompare(lastnames.get(b));
});

answered Jan 18, 2022 at 14:27

T.J. Crowder

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1 Comment

fokicheva Over a year ago

Thank you, this explanation is really great, and I appreciate being given multiple options! Both educational AND applicable, thank you very much!

sefa · Accepted Answer · 2022-01-18 14:28:12Z

2

You are just declaring a new variable trying to access it via object's property. You should map your data in the first place like:

const names = [
    {
        firstname: "John",
        fullname: "John Doe"
    },
    {
        firstname: "Amber",
        fullname: "Amber Smith"
    },
    {
        firstname: "Michael",
        fullname: "Michael Smith"
    },
    {
        firstname: "Jessica",
        fullname: "Jessica Kelly Charles"
    }
].map(person => ({
    ...person, 
    lastName: person.fullName.replace(person.firstName + ' ', '')
}));

After mapping your data like that, you can use .lastName in the place you need.

names.sort(function(a, b) {
    if (a.lastName < b.lastName) {
        return -1;
    } else if (a.lastName > b.lastName) {
        return 1;
    }
    return 0;
});

answered Jan 18, 2022 at 14:28

sefa

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1 Comment

Shay Yzhakov Over a year ago

Exactly. You have to prepare your data beforehand in order to achieve what you want

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