TheAlgorithms/JavaScript · error · TypeError

Given input is not an array

Error message

Given input is not an array

What it means

Thrown as a TypeError by selectionSort() when the input list is not an array. The function spreads the input ([...list]) and indexes it, so a non-array would either spread incorrectly or fail. This is the outer type guard; a separate inner check (error 130) validates element types.

Source

Thrown at Sorts/SelectionSort.js:13

/* The selection sort algorithm sorts an array by repeatedly finding the minimum element
 *(considering ascending order) from unsorted part and putting it at the beginning. The
 *algorithm maintains two subarrays in a given array.
 *1) The subarray which is already sorted.
 *2) Remaining subarray which is unsorted.
 *
 *In every iteration of selection sort, the minimum element (considering ascending order)
 *from the unsorted subarray is picked and moved to the sorted subarray.
 */

export const selectionSort = (list) => {
  if (!Array.isArray(list)) {
    throw new TypeError('Given input is not an array')
  }
  const items = [...list] // We don't want to modify the original array
  const length = items.length
  for (let i = 0; i < length - 1; i++) {
    if (typeof items[i] !== 'number') {
      throw new TypeError('One of the items in your array is not a number')
    }
    // Number of passes
    let min = i // min holds the current minimum number position for each pass; i holds the Initial min number
    for (let j = i + 1; j < length; j++) {
      // Note that j = i + 1 as we only need to go through unsorted array
      if (items[j] < items[min]) {
        // Compare the numbers
        min = j // Change the current min number position if a smaller num is found
      }
    }
    if (min !== i) {
      // After each pass, if the current min num != initial min num, exchange the position.

View on GitHub (pinned to 5c39e87a9a)

Solutions

1. Convert array-like objects: selectionSort(Array.from(nodeList)).
2. Guard at the boundary: if (!Array.isArray(x)) throw new TypeError('expected array').
3. Coerce strings if numeric sorting is intended: selectionSort([...str].map(Number)).

Example fix

// before
const sorted = selectionSort(maybeString)

// after
const arr = Array.isArray(maybeString) ? maybeString : Array.from(maybeString)
const sorted = selectionSort(arr)

function safeSelectionSort(list) {
  if (!Array.isArray(list)) {
    throw new TypeError('Expected an array')
  }
  return selectionSort(list)
}

function isArray(v) {
  return Array.isArray(v)
}

try {
  selectionSort(list)
} catch (e) {
  if (e instanceof TypeError && e.message === 'Given input is not an array') {
    return selectionSort(Array.from(list))
  }
  throw e
}

When it happens

Trigger: Calling selectionSort(null), selectionSort(undefined), selectionSort('dcba'), selectionSort(4321), or selectionSort({0:3}). Passing a string is common because strings are array-like but not arrays.

Common situations: User input from a text field passed unmodified; a value that is sometimes null from a lookup; treating a NodeList as an array without conversion.

Related errors

• Please input a valid list or array.
• One of the items in your array is not a number
• The ${paramName} should be type Number
• Type of n must be number
• Invalid Input

AI-assisted analysis of TheAlgorithms/JavaScript@5c39e87a9a (2026-08-13). Data as JSON: /api/errors/a564838613ef13c4. Report an issue: GitHub.