CODEWITHSUNDEEP
sveltesvelte-3svelte-componentsvelte-store
rohanharikr
rohanharikr

Reputation: 1811

How to trigger a function when there is a value change in subscribed store in Svelte?

One of my components is subscribed to a variable in a store. Whenever there is a change in that store var, I want to trigger a function.

stores.js

    import { writable } from "svelte/store"; 
    export const comparedProducts = writable([1,2,3]);

Component.svelte

    import { comparedProducts } from "../stores.js";
    
    //if there is a change in $comparedProducts trigger this function eg. ([1,2])
    const someFunction = () => {
      //do something
    }

Upvotes: 13

Views: 12885

Answers (5)

brunnerh
brunnerh

Reputation: 185290

If the function uses the store, it can be declared and called reactively. Variables used within the function then will be tracked as dependencies.

$: someFunction = () => { /* ... */ }
$: someFunction();

In Svelte 5, reactivity crosses function boundaries automatically (via signals), so things like this are not necessary there.

Upvotes: 0

Jonathan
Jonathan

Reputation: 4709

Adding to @rohanharikr's answer

$: $comparedProducts, (() => {
  // do something here
})();

You can make an anonymous function which will automatically create and unsubscribe to the function.

Upvotes: 2

Emcog
Emcog

Reputation: 1

More detail and working Repl demoing a counter.

store.js

import { writable } from "svelte/store"; 
export const count = writable(0);

Component.svelte

import { count } from "../store.js";
$: if($count > 0) { foo($count) }

    
function foo($count) {
   console.log($count)
}

Upvotes: 0

rohanharikr
rohanharikr

Reputation: 1811

Found a cleaner solution

import { comparedProducts } from "../stores.js";
$: $comparedProducts, run();

function run(){
  //do something here
}

Upvotes: 28

OmG3r
OmG3r

Reputation: 1821

in componenet.svelte

    import { comparedProducts } from "../stores.js";
    
    //if there is a change in $comparedProducts trigger this function eg. ([1,2])
    const someFunction = () = >{
      // do something
    }
    
    // stores can be subscribed to using .subscribe()
    // each new value will trigger the callback supplied to .subscribe()
    
    let unsubscribeStore = comparedProducts.subscribe((currentValue) => {
        //currentValue == $comparedProducts
        someFunction()
    })

    // call unsubscribeStore() after finishing to stop listening for new values

Upvotes: 8

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