Box
Box your state and take it anywhere
Description
Runes for state are primitives. They provide a concise syntax for local reactivity. However, when we send these state primitives across boundaries (e.g. in function arguments), the state loses it's reactivity and becomes a static value.
Boxes provide several utilities to make passing reactive state across boundaries easier.
Usage
box
Initializes a writable boxed state.
<script lang="ts">
import { box } from "runed";
const count = box(0);
</script>
<button onclick={() => count.value++}>
clicks: {count.value}
</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.value++;
},
// We pass a box that doubles the count value
double: box.with(() => count.value * 2)
};
}
let count = $state(0);
// We pass count to box.with so it stays in sync
const { double, increment } = useCounter(
box.with(
() => count.value,
(v) => (count = v)
)
);
</script>
<button onclick={increment}>
clicks: {count}
double: {double.value}
</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.value++;
},
// We pass a box that doubles the count value
double: box.with(() => count.value * 2)
};
}
const counter1 = useCounter(1);
console.log(counter1.count.value); // 1
console.log(counter1.double.value); // 2
const counter2 = useCounter(box(2));
console.log(counter2.count.value); // 2
console.log(counter2.double.value); // 4
function useDouble(_count: number | (() => number) | ReadableBox<number>) {
const count = box.from(_count);
return box.with(() => count.value * 2);
}
const double1 = useDouble(1);
console.log(double1.value); // 2
const double2 = useDouble(box(2));
console.log(double2.value); // 4
const double3 = useDouble(() => counter1.count.value);
console.log(double3.value); // 2
</script>
box.flatten
Transforms any boxes within an object to reactive properties, removing the need to access each
property with .value.
const count = box(1);
const flat = box.flatten({
count,
double: box.with(() => count.value * 2),
increment() {
count.value++;
}
});
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.value); // 1
count.value++;
console.log(readonlyCount.value); // 2
readonlyCount.value = 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.value * 2);
console.log(box.isWritableBox(count)); // true
console.log(box.isWritableBox(double)); // false