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Sum input numbers

importance: 4

Write the function sumInput() that:

  • Asks the user for values using prompt and stores the values in the array.
  • Finishes asking when the user enters a non-numeric value, an empty string, or presses “Cancel”.
  • Calculates and returns the sum of array items.

P.S. A zero 0 is a valid number, please don’t stop the input on zero.

Run the demo

Please note the subtle, but important detail of the solution. We don’t convert value to number instantly after prompt, because after value = +value we would not be able to tell an empty string (stop sign) from the zero (valid number). We do it later instead.

function sumInput() {

  let numbers = [];

  while (true) {

    let value = prompt("A number please?", 0);

    // should we cancel?
    if (value === "" || value === null || !isFinite(value)) break;


  let sum = 0;
  for (let number of numbers) {
    sum += number;
  return sum;

alert( sumInput() );