TheAlgorithms/JavaScript · error · TypeError

Expected integer N and finite a, b

Error message

Expected integer N and finite a, b

What it means

The integralEvaluation function approximates a definite integral using the midpoint rule with N subintervals. The guard requires N to be an integer and a, b to be non-NaN. Important caveat: the code uses Number.isNaN(a) rather than !Number.isFinite(a), so Infinity would pass this check and could cause silent numerical issues downstream. Subsequent checks enforce N > 0 and a <= b.

Source

Thrown at Maths/MidpointIntegration.js:23

 * @brief Calculate definite integrals with midpoint method
 *
 * @details The idea is to split the interval in a number N of intervals and use as interpolation points the xi
 * for which it applies that xi = x0 + i*h, where h is a step defined as h = (b-a)/N where a and b are the
 * first and last points of the interval of the integration [a, b].
 *
 * We create a table of the xi and their corresponding f(xi) values and we evaluate the integral by the formula:
 * I = h * {f(x0+h/2) + f(x1+h/2) + ... + f(xN-1+h/2)}
 *
 * N must be > 0 and a<b. By increasing N, we also increase precision
 *
 * [More info link](https://tutorial.math.lamar.edu/classes/calcii/approximatingdefintegrals.aspx)
 *
 */

function integralEvaluation(N, a, b, func) {
  // Check if all restrictions are satisfied for the given N, a, b
  if (!Number.isInteger(N) || Number.isNaN(a) || Number.isNaN(b)) {
    throw new TypeError('Expected integer N and finite a, b')
  }
  if (N <= 0) {
    throw Error('N has to be >= 2')
  } // check if N > 0
  if (a > b) {
    throw Error('a must be less or equal than b')
  } // Check if a < b
  if (a === b) return 0 // If a === b integral is zero

  // Calculate the step h
  const h = (b - a) / N

  // Find interpolation points
  let xi = a // initialize xi = x0
  const pointsArray = []

  // Find the sum {f(x0+h/2) + f(x1+h/2) + ... + f(xN-1+h/2)}
  let temp

View on GitHub (pinned to 5c39e87a9a)

Solutions

1. Ensure N is an integer (use Math.round or parseInt).
2. Validate a and b are finite numbers before calling.
3. Parse string config values to numbers before invoking.

Example fix

// before
integralEvaluation((b - a) / h, a, b, f)
// after
integralEvaluation(Math.round((b - a) / h), a, b, f)

if (!Number.isInteger(N) || !Number.isFinite(a) || !Number.isFinite(b)) {
  throw new TypeError('Expected integer N and finite a, b')
}
integralEvaluation(N, a, b, func)

const isValidIntegrationInput = (N, a, b) => Number.isInteger(N) && Number.isFinite(a) && Number.isFinite(b)

When it happens

Trigger: Calling integralEvaluation(1.5, 0, 1, f) (non-integer N), integralEvaluation(10, NaN, 1, f) (NaN a), or integralEvaluation("10", 0, 1, f) (string N, since Number.isInteger("10") is false).

Common situations: N computed as a non-integer from a division (e.g., (b-a)/h), NaN from undefined interval bounds, or string arguments read from a configuration file.

Related errors

• Expected integer N and finite a, b
• Index cannot be a Decimal
• Expected a number, received ${typeof num}
• Expected a number, received ${typeof precision}
• Input data must be numbers

AI-assisted analysis of TheAlgorithms/JavaScript@5c39e87a9a (2026-08-13). Data as JSON: /api/errors/d337dfdf06449f6f. Report an issue: GitHub.