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Adding
Indexing
Transforming
Mutate a signal holding an array and notify dependents in one call. These helpers change the stored array in place, so they work under the default safety: 'reference' without needing a fresh reference.
Unlike set, most of these helpers skip the equality check and notify dependents unconditionally. The exception is setIndex, which notifies only when the indexed value changes.
Unlike set, most of these helpers skip the equality check and notify dependents unconditionally. The exception is setIndex, which notifies only when the indexed value changes.
Adding
push
signal.push(...items);Adds one or more elements to the end of the array.
Parameters
| Name | Type | Description |
|---|---|---|
| …items | any | Elements to append |
Usage
const fruits = signal(['apple']);fruits.push('banana'); // ['apple', 'banana']fruits.push('orange', 'grape'); // ['apple', 'banana', 'orange', 'grape']Example
unshift
signal.unshift(...items);Adds one or more elements to the beginning of the array.
Parameters
| Name | Type | Description |
|---|---|---|
| …items | any | Elements to prepend |
Usage
const numbers = signal([3]);numbers.unshift(1, 2); // [1, 2, 3]Example
splice
signal.splice(start, deleteCount, ...items);Removes or replaces existing elements and inserts new ones, matching Array.prototype.splice.
Parameters
| Name | Type | Description |
|---|---|---|
| start | number | Index at which to start changing the array |
| deleteCount | number | Number of elements to remove. Optional |
| …items | any | Elements to insert. Optional |
Usage
const colors = signal(['red', 'green', 'blue']);colors.splice(1, 1, 'yellow'); // ['red', 'yellow', 'blue']Example
Indexing
setIndex
signal.setIndex(index, value);Sets the value at a specific index. Notifies dependents only when the value differs from the current one by ===.
Parameters
| Name | Type | Description |
|---|---|---|
| index | number | Index to write |
| value | any | Value to store at the index |
Usage
const items = signal(['a', 'b', 'c']);items.setIndex(1, 'x'); // ['a', 'x', 'c']Example
removeIndex
signal.removeIndex(index);Removes the element at a specific index.
Parameters
| Name | Type | Description |
|---|---|---|
| index | number | Index of the element to remove |
Usage
const letters = signal(['a', 'b', 'c']);letters.removeIndex(1); // ['a', 'c']Example
getIndex
signal.getIndex(index);Reads the element at a specific index and subscribes the running reaction, like get.
Parameters
| Name | Type | Description |
|---|---|---|
| index | number | Index of the element to read |
Returns
The element at index.
Example
Transforming
map
signal.map(callback);Replaces each element with the callback’s return value, in place. Unlike Array.prototype.map this writes back into the signal rather than returning a new array.
Parameters
| Name | Type | Description |
|---|---|---|
| callback | function | Receives (value, index, array), returns the replacement element |
Usage
const numbers = signal([1, 2, 3]);numbers.map(n => n * 2); // [2, 4, 6]Example
filter
signal.filter(predicate);Keeps only the elements that pass the predicate, in place. Unlike Array.prototype.filter this narrows the stored array rather than returning a new one.
Parameters
| Name | Type | Description |
|---|---|---|
| predicate | function | Receives (value, index, array), returns whether to keep the element |
Usage
const numbers = signal([1, 2, 3, 4, 5]);numbers.filter(n => n % 2 === 0); // [2, 4]