TheAlgorithms/JavaScript · error · TypeError

Invalid Input

Error message

Invalid Input

What it means

Thrown by mean(numbers) (AverageMean.js:14) as a TypeError when the argument is not an array (Array.isArray returns false). This is the first of three validation checks in mean: non-array throws here, empty array throws separately, and non-number elements throw inside the loop. The function expects a single array argument, not spread/rest arguments.

Source

Thrown at Maths/AverageMean.js:14

/**
 * @function mean
 * @description This script will find the mean value of a array of numbers.
 * @param {number[]} numbers - Array of integer
 * @return {number} - mean of numbers.
 * @throws {TypeError} If the input is not an array or contains non-number elements.
 * @throws {Error} If the input array is empty.
 * @see [Mean](https://en.wikipedia.org/wiki/Mean)
 * @example mean([1, 2, 4, 5]) = 3
 * @example mean([10, 40, 100, 20]) = 42.5
 */
const mean = (numbers) => {
  if (!Array.isArray(numbers)) {
    throw new TypeError('Invalid Input')
  } else if (numbers.length === 0) {
    throw new Error('Array is empty')
  }

  let total = 0
  numbers.forEach((num) => {
    if (typeof num !== 'number') {
      throw new TypeError('Invalid Input')
    }
    total += num
  })

  return total / numbers.length
}

export { mean }

View on GitHub (pinned to 5c39e87a9a)

Solutions

1. Wrap the arguments in an array literal: mean([1, 2, 3]) not mean(1, 2, 3).
2. Convert array-likes with Array.from() or spread: mean([...mySet]).
3. Guard the call: if (!Array.isArray(x)) return NaN or convert.
4. If the value may be undefined from optional chaining, default it: mean(data ?? []).

Example fix

// before
const m = mean(...values) // spreads into separate args, not an array

// after
const m = mean(Array.isArray(values) ? values : [values])
// or simply:
const m = mean(values) // pass the array directly

if (!Array.isArray(data)) {
  data = Array.from(data) // for iterables, or wrap single values
}
const m = mean(data)

const isNumberArray = (v) => Array.isArray(v) && v.every(x => typeof x === 'number')

try {
  m = mean(numbers)
} catch (e) {
  if (e instanceof TypeError && e.message === 'Invalid Input') {
    // not an array — convert and retry
  } else throw e
}

When it happens

Trigger: Call mean(1, 2, 3) (passing spread args instead of an array); mean('123') passing a string; mean({length: 3}) passing an array-like object; mean(42) passing a scalar; mean(null) from a missing field.

Common situations: Confusing mean([1,2,3]) with mean(1,2,3) — the function is not variadic; passing a Set or Map that must be spread to an array first; passing arguments object from a legacy function; receiving undefined from a failed JSON lookup.

Related errors

• Invalid Input
• Argument must be an Array
• Invalid Input
• The ${paramName} should be type Number
• Type of n must be number

AI-assisted analysis of TheAlgorithms/JavaScript@5c39e87a9a (2026-08-13). Data as JSON: /api/errors/e302af1f96f0c73d. Report an issue: GitHub.