How to fix Property 'item' does not exist on type 'Record' error?

Question

typescript

for(let item in classes){
    classes.item = 'page'+item
  }

Answer 1

First: as YavaDev rightly pointed out : classes[item].
Secondly: only manually, at your own peril and risk:

for(let item in classes) {
    classes[item as keyof typeof classes] = 'page'+item
}

Typescript did not specifically add automatic typing of keys, leaving it simple string, because due to its structural nature it is impossible to say for sure whether the resulting object (or its prototype) has any other keys other than those specified in its type, and, accordingly, you can not be sure that nothing will break.

Answer 2

You need to add the item property to the Record type