Unit 5 · Data and algorithms
Array vs object: which one to use
Use an array for a list where position matters: a queue, a ranking, steps in order. Use an object for one record whose facts have names: a contact with a name, a phone and an email.
The mix-up
What people often think
“A contact is a list of things about a person, so it is an array.”
What the tutor says
In an array you would have to remember that position 1 is the phone. An object lets you ask for contact.phone by name.
Which is easier to read later: friend[2] or friend.email?
How it works
Storing a contact as an array means remembering that position 1 is the phone. friend.email is easier to read later than friend[2].
Objects have no positions, only keys. The key is the label you look up by (phone); the value is what you get back (the number). For a top 10, the position is the meaning, so an array already numbers every song for you.
An example
const topSongs = ["Song A", "Song B", "Song C"]; // order matters
const contact = { name: "Priya", phone: "555-0142" }; // named facts
topSongs[0]; // number one
contact.phone; // "555-0142"Close cousins of this mix-up
The tutor watches for these in the same lesson.
“A top 10 needs names for each place, so it is an object.”
The position is the meaning here. An array already numbers every song in order, so songs[0] is number one.
“Objects are numbered like arrays.”
An object has no positions, only names. Ask for the fact by its key: contact.phone.
“The phone number is the key, because it is the thing you want.”
The key is the label you look things up by: phone. The value is what you get back: the number itself.
Practise it with a tutor watching
Arrays and objects
Store a list in an array, a record in an object, and read any item back out.
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