Unexpected reactivity

[MrRobu]

View in REPL

[Axelen123]

It's because svelte reacts when you reassign (example: array = array[..array, value]), not when you update the value (example: array.push(value)).

Example REPL

[btk5h]

Self-assignment is a documented workaround to force Svelte to update mutable objects.

You can use <svelte:options immutable/> to make Svelte use referential equality checks for objects. REPL

[MrRobu]

It's because svelte reacts when you reassign (example: array = array[..array, value]), not when you update the value (example: array.push(value)).

Example REPL

But why reacts if is the same value (pointer to that array)? And why reacts to the same value only to arrays and not other value types?

[MrRobu]

Self-assignment is a documented workaround to force Svelte to update mutable objects.

You can use <svelte:options immutable/> to make Svelte use referential equality checks for objects. REPL

Ok, so that tag is the solution for the select. But why it reacts if I don't touch the array when i select an item?

[Axelen123]

But why reacts if is the same value (pointer to that array)?

Svelte doesn't store and compare the value. When you write this:

let value = "something";
value = "foo";

The svelte compiler turns it into something like this:

let value = "something";
value = "foo"; $$invalidate("value");

$$invalidate() basically tells svelte that the variabler was reassigned.

And why reacts to the same value only to arrays and not other value types?

The type does not matter.
I could make an example with objects but I an on my phone right now :/

[MrRobu]

Ok, objects behave the same. But strings, numbers, bools why don't react if I reassign with the same value?

…

On Fri, 21 Jun 2019, 16:49 Ax333l, ***@***.***> wrote: But why reacts if is the same value (pointer to that array)? Svelte doesn't store and compare the value. When you write this: let value = "something"; value = "foo"; The svelte compiler turns it into something like this: let value = "something"; value = "foo"; $$invalidate("value"); $$invalidate() basically tells svelte that the variabler was reassigned. And why reacts to the same value only to arrays and not other value types? The type does not matter. I could make an example with objects but I an on my phone right now :/ — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#3065?email_source=notifications&email_token=AI25BMSCOZBPHRH63WOWSQDP3TL6JA5CNFSM4H2NRH5KYY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGODYIQOGQ#issuecomment-504432410>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AI25BMS36SEMVSZWM2KW7FLP3TL6JANCNFSM4H2NRH5A> .

[btk5h]

Checkout the source code for safe_not_equal. Objects are always considered unequal unless you use the immutable option to allow referential equality for objects.