Svelte Toolbelt
Utilities for Svelte 5 that I find useful and will use in the various projects I work on. It's maintained by me, for me.
For more robust and feature-rich utilities, I recommend checking out/using runed.
Installation
npm install svelte-toolbelt
Box
box
Initializes a writable boxed state.
<script lang="ts">
import { box } from "runed";
const count = box(0);
</script>
<button onclick={() => count.current++}>
clicks: {count.current}
</button>
box.with
Creates reactive state using getter and setter functions. If a setter function is provided, the box is writable. If not, the box is readonly.
Useful for passing synced reactive values across boundaries.
<script lang="ts">
import { type WritableBox, box } from "runed";
function useCounter(count: WritableBox<number>) {
return {
increment() {
count.current++;
},
// We pass a box that doubles the count value
double: box.with(() => count.current * 2)
};
}
let count = $state(0);
// We pass count to box.with so it stays in sync
const { double, increment } = useCounter(
box.with(
() => count.current,
(v) => (count = v)
)
);
</script>
<button onclick={increment}>
clicks: {count}
double: {double.current}
</button>
box.from
Creates a box from an existing box, a getter function, or a static value.
Useful for receiving arguments that may or may not be reactive.
<script lang="ts">
import { box } from "runed";
function useCounter(_count: WritableBox<number> | number) {
const count = box.from(_count);
return {
count,
increment() {
count.current++;
},
// We pass a box that doubles the count value
double: box.with(() => count.current * 2)
};
}
const counter1 = useCounter(1);
console.log(counter1.count.current); // 1
console.log(counter1.double.current); // 2
const counter2 = useCounter(box(2));
console.log(counter2.count.current); // 2
console.log(counter2.double.current); // 4
function useDouble(_count: number | (() => number) | ReadableBox<number>) {
const count = box.from(_count);
return box.with(() => count.current * 2);
}
const double1 = useDouble(1);
console.log(double1.current); // 2
const double2 = useDouble(box(2));
console.log(double2.current); // 4
const double3 = useDouble(() => counter1.count.current);
console.log(double3.current); // 2
</script>
box.flatten
Transforms any boxes within an object to reactive properties, removing the need to access each
property with .current.
const count = box(1);
const flat = box.flatten({
count,
double: box.with(() => count.current * 2),
increment() {
count.current++;
}
});
console.log(flat.count); // 1
console.log(flat.double); // 2
flat.increment();
console.log(flat.count); // 2
box.readonly
Creates a readonly box from a writable box that remains in sync with the original box.
const count = box(1);
const readonlyCount = box.readonly(count);
console.log(readonlyCount.current); // 1
count.current++;
console.log(readonlyCount.current); // 2
readonlyCount.current = 3; // Error: Cannot assign to read only property 'value' of object
box.isBox
Checks if a value is a Box.
const count = box(1);
console.log(box.isBox(count)); // true
console.log(box.isBox(1)); // false
box.isWritableBox
Checks if a value is a WritableBox.
const count = box(1);
const double = box.with(() => count.current * 2);
console.log(box.isWritableBox(count)); // true
console.log(box.isWritableBox(double)); // false
unbox
Unboxes the value from a box.
const count = box(1);
const double = box.with(() => count.current * 2);
console.log(unbox(double)); // 2
Utils
afterSleep
Executes a callback after a specified number of milliseconds.
afterSleep(1000, () => console.log("Hello, world!"));
afterTick
Executes a callback after the next tick.
afterTick(() => console.log("Hello, world!"));
composeHandlers
Composes event handlers into a single function that can be called with an event.
If the previous handler cancels the event using event.preventDefault(), the handlers
that follow will not be called.
import { composeHandlers } from "svelte-toolbelt";
const handler1 = () => console.log("Handler 1");
const handler2 = () => console.log("Handler 2");
const composedHandler = composeHandlers(handler1, handler2);
const event = new MouseEvent("click", { cancelable: true });
console.log(composedHandler(event)); // Handler 1, Handler 2
cssToStyleObj
Converts a CSS string to a style object.
const css = "color: red; font-size: 16px;";
const styleObj = cssToStyleObj(css);
console.log(styleObj); // { color: "red", fontSize: "16px" }
executeCallbacks
Executes an array of callback functions with the same arguments.
const callback1 = () => console.log("Callback 1");
const callback2 = () => console.log("Callback 2");
console.log(executeCallbacks(callback1, callback2)); // Callback 1, Callback 2
addEventListener
Adds an event listener to the specified target element(s) for the given event(s), and returns a function to remove it.
import { addEventListener } from "svelte-toolbelt";
const target = document.getElementById("my-element");
const event = "click";
const handler = () => console.log("Clicked!");
const removeListener = addEventListener(target, event, handler);
// Later, remove the listener
removeListener();
mergeProps
Merges props into a single object.
import { mergeProps } from "svelte-toolbelt";
const props1 = { a: 1 };
const props2 = { b: 2 };
const result = mergeProps(props1, props2);
console.log(result); // { a: 1, b: 2 }
Event Handlers
Event handlers are chained in the order they're passed. If a handler calls event.preventDefault(), subsequent handlers in the chain are not executed.
const props1 = { onclick: (e: MouseEvent) => console.log("First click") };
const props2 = { onclick: (e: MouseEvent) => console.log("Second click") };
const mergedProps = mergeProps(props1, props2);
mergedProps.onclick(new MouseEvent("click")); // Logs: "First click" then "Second click"
If preventDefault() is called:
const props1 = { onclick: (e: MouseEvent) => console.log("First click") };
const props2 = {
onclick: (e: MouseEvent) => {
console.log("Second click");
e.preventDefault();
}
};
const props3 = { onclick: (e: MouseEvent) => console.log("Third click") };
const mergedProps = mergeProps(props1, props2, props3);
mergedProps.onclick(new MouseEvent("click")); // Logs: "First click" then "Second click" only
Since props2 called event.preventDefault(), props3's onclick handler will not be called.
Non-Event Handler Functions
Non-event handler functions are also chained, but without the ability to prevent subsequent functions from executing:
const props1 = { doSomething: () => console.log("Action 1") };
const props2 = { doSomething: () => console.log("Action 2") };
const mergedProps = mergeProps(props1, props2);
mergedProps.doSomething(); // Logs: "Action 1" then "Action 2"
Classes
Class names are merged using clsx:
const props1 = { class: "text-lg font-bold" };
const props2 = { class: ["bg-blue-500", "hover:bg-blue-600"] };
const mergedProps = mergeProps(props1, props2);
console.log(mergedProps.class); // "text-lg font-bold bg-blue-500 hover:bg-blue-600"
Styles
Style objects and strings are merged, with later properties overriding earlier ones:
const props1 = { style: { color: "red", fontSize: "16px" } };
const props2 = { style: "background-color: blue; font-weight: bold;" };
const mergedProps = mergeProps(props1, props2);
console.log(mergedProps.style);
// "color: red; font-size: 16px; background-color: blue; font-weight: bold;"
import { mergeProps } from "bits-ui";
const props1 = { style: "--foo: red" };
const props2 = { style: { "--foo": "green", color: "blue" } };
const mergedProps = mergeProps(props1, props2);
console.log(mergedProps.style); // "--foo: green; color: blue;"
onDestroyEffect
Executes a callback when a component is destroyed.
onMountEffect
Executes a callback when a component is mounted.
styleToString
Converts a style object to a CSS string.
const style = { color: "red", fontSize: "16px" };
const css = styleToString(style);
console.log(css); // "color: red; font-size: 16px;"
srOnlyStyles
An object of styles that can be used to hide content from the DOM but still be accessible to screen readers.
export const srOnlyStyles: StyleProperties = {
position: "absolute",
width: "1px",
height: "1px",
padding: "0",
margin: "-1px",
overflow: "hidden",
clip: "rect(0, 0, 0, 0)",
whiteSpace: "nowrap",
borderWidth: "0",
transform: "translateX(-100%)"
};
srOnlyStylesString
A string representation of srOnlyStyles.
useRefById
Finds the node with the given boxed id and sets it to the boxed ref. Reactive using $effect to ensure when the id or deps change, an update is triggered and the node is re-found.
Props
type UseRefByIdProps = {
/**
* The ID of the node to find.
*/
id: Box<string>;
/**
* The ref to set the node to.
*/
ref: WritableBox<HTMLElement | null>;
/**
* A reactive condition that will cause the node to be set.
*/
deps?: Getter<unknown>;
/**
* A callback fired when the ref changes.
*/
onRefChange?: (node: HTMLElement | null) => void;
/**
* A function that returns the root node to search for the element by ID.
* Defaults to `() => (typeof document !== "undefined" ? document : undefined)
*/
getRootNode?: Getter<Document | ShadowRoot | undefined>;
};
useOnChange
A simple helper function to react to changes to reactive state. This is useful for syncing a read-only dependency that may change with some writable state in your app.
<script lang="ts">
import { useOnChange } from "svelte-toolbelt";
let { data } = $props();
let myData = $state(data);
useOnChange(
() => myData,
(newData) => (myData = newData)
);
</script>
