FAQ: Arrays - Update Elements

This community-built FAQ covers the "Update Elements " exercise from the lesson “Arrays”.

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This exercise can be found in the following Codecademy content:

Web Development

Introduction To JavaScript

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Why can’t I just delete fall in the var at the beginning and write Autumn instead of writing a new command to replace it? Isn’t that just creating redundant code?


Dont quote me but im guessing its for if you want the code to be fall when its first read but then change to autumn later, im guessing theres a use for it somewhere i havent googled.

I changed the type of the groceryList to const, and still can change the elements of the array without errors, despite it is constant. as below, so how come?

const groceryList = [‘bread’, ‘tomatoes’, ‘milk’];

groceryList [1] = ‘avocados’;


// output: [ ‘bread’, ‘avocados’, ‘milk’ ]


had the same question… Please reply ASAP

You can change the content of an array assigned to a const variable, and the type of variable would still be an array and the array, the list would be the same, just different content.

You can think of it as a list on a piece of paper you named List1, but you erased an item and wrote something else in place.

What you would’t be allowed to do, is to turn this variable into another array or another type of variable, say a boolean or a string.

Like you can’t take another piece of paper or a rock and call it List1.

Don’t trust me blindly, I’m also learning.

Nice question, When you use const for a collection variable(group of elements under one variable (like array or objects) ), You can still edit the values of the collection… But when you use const for single variable , you cannot update its values…

In documentation says this in crisp way i.e const cannot be re-assigned or re-declared …

//+ Possible updation in collection

const x = {};

x.foo = 'bar';
console.log(x); // {foo : 'bar'}

x.foo = 'bar2';
console.log(x); // {foo : 'bar2'}  

const y = [];
console.log(y); // ['foo']

console.log(y); // ['foo2', 'foo']

console.log(y); // ['foo2']

Updation not possible for non-collections.

const x = {};
x = {foo: 'bar'}; // error - re-assigning

const y = ['foo'];
const y = ['bar']; // error - re-declaring

const foo = 'bar'; 
foo = 'bar2';       // error - can not re-assign

var foo = 'bar3';   // error - cannot re-declare
function foo() {};  // error - cannot re-declare

I hope you are understood now !

1 Like

yeah you can do that… But the purpose of this tutorial to learn updation of element in array … changing values straight in the input array is not called updation.

I love your explanation! But then which should we rather use for defining array variables? ‘let’ or ‘const’?

Its based on the usage…If you want to re-declare the variable content , use let otherwise use const…

why does the below code log “bread, avocados and milk” to the console?

let groceryList = [‘bread’, ‘tomatoes’, ‘milk’];
groceryList[1] = “avocados”;

BUT the code below logs only “avocados” to the console

let groceryList = [‘bread’, ‘tomatoes’, ‘milk’];

let modifiedGroceryList = groceryList[1] = “avocados”

Thanks you