For AI agents: the complete documentation index is available at /llms.txt, the full documentation bundle is available at /llms-full.txt, and this page is available as Markdown at /reference/array/adjust.md.
Install massaman

    adjust

    Applies a function to the element at an index and returns a new array.

    const adjusted = adjust([1, 2, 3], 1, (value) => value * 10)
// [1, 20, 3]

    Usage

    adjust(array, index, fn)

    Use adjust when one position needs to change without mutating the input array. The callback runs only when index is within the array bounds; an out-of-bounds index returns an unchanged copy.

    import { adjust } from 'massaman'
// or:  import { adjust } from 'massaman/array'

const original = [1, 2, 3]
const adjusted = adjust(original, 1, (value) => value * 10)

console.log(original) // [1, 2, 3]
console.log(adjusted) // [1, 20, 3]

    Parameters

    arrayreadonly T[]required

    the source array. It is never mutated.

    indexnumberrequired

    the zero-based index of the element to transform.

    fn(value: T) => Trequired

    the function applied to the element at index.

    Returns

    a new array containing the transformed element. When index is negative or greater than or equal to the array length, the returned copy has the same elements as array.

    T[]

    Examples

    import { adjust } from 'massaman/array'

type Task = Readonly<{
  title: string
  completed: boolean
}>

const tasks: readonly Task[] = [
  { title: 'Write docs', completed: false },
  { title: 'Ship release', completed: false },
]

const completed = adjust(tasks, 0, (task) => ({
  ...task,
  completed: true,
}))

console.log(completed[0])
// { title: 'Write docs', completed: true }