conditional "if" "else" statement for string "number" and real "number"

Question

I am attempting to make a conditional statement where the code will only run if it is a real number 90 vs a string number "90". I don't know what to type into the number part in my conditional statement. I have tried using Number and I have also tried variations of typeof() method. My code is listed below. Thank you

        function sumAll(start, end) {
            let x = 0;
            array = [];

            if (start === Number && end === Number) {
                if (start < end && start >= 0) {

                    for (let i = start; i <= end; i++) {
                        array.push(i);
                        console.log(array);
                        x = i + x;
                    }
                    return x;

                } else if (start > end) {
                    for (let i = start; i >= end; i--) {
                        array.push(i);
                        // console.log(array);
                        x = i + x;
                    }
                    return x;
                } else {
                    return 'ERROR';
                }
            } else {
                return 'ERROR not a number';
            }
        }


        console.log(sumAll(10, 90));
        sumAll(10, "90")
        // expect(sumAll(10, "90")).toEqual('ERROR');
    ```

Angel · Accepted Answer · 2020-07-14 11:03:26Z

2

let n = 5;

console.log(n === Number);
console.log(typeof n === "number");

The first one logs false, the second one true. You should try using typeof to check if start and end are numbers in your code.

answered Jul 14, 2020 at 11:03

Angel

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Comments

crashmstr · Accepted Answer · 2020-07-14 11:05:36Z

1

You need to use the typeof operator

Using it, you can check to see if start and end are 'number'

function sumAll(start, end) {
  let x = 0;
  array = [];

  if (typeof start === 'number' && typeof end === 'number') {
    if (start < end && start >= 0) {

      for (let i = start; i <= end; i++) {
        array.push(i);
        console.log(array);
        x = i + x;
      }
      return x;

    } else if (start > end) {
      for (let i = start; i >= end; i--) {
        array.push(i);
        // console.log(array);
        x = i + x;
      }
      return x;
    } else {
      return 'ERROR';
    }
  } else {
    return 'ERROR not a number';
  }
}


console.log(sumAll(10, 90));
console.log(sumAll(10, "90"));
// expect(sumAll(10, "90")).toEqual('ERROR');}

answered Jul 14, 2020 at 11:05

crashmstr

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2 Comments

coe Over a year ago

I typed in the typeof wrong originally when I tried it. Any tips for learning the syntax of how to type this stuff in correctly?

crashmstr Over a year ago

I've used Mozilla's MDN a lot for reference as well as stackoverflow. Both of those often help me find how to do what I'm trying to do, especially when it comes to new syntax.

Abror Abdullaev · Accepted Answer · 2020-07-14 11:20:23Z

I think you used typeof wrongly, because that is the answer you need here.

const a = 5;
const b = '5';

if (typeof a === 'number') { } //true
if (typeof a === 'string') { } //false

if (typeof b === 'number') { } //false
if (typeof b === 'string') { } //true


console.log('type of a: ', typeof a);
console.log('type of b: ', typeof b);

But it seems like you can use string '90' as well converting it into number.

function sumAll(start, end) {
  let x = 0;
  array = [];

  if (typeof start === 'string') { start = parseInt(start, 10); } // case '90'
  if (typeof end === 'string') { end = parseInt(end, 10); } // case '90'

  if (Number.isNaN(start) || Number.isNaN(end)) {
    // Error case
    return 'Error not a number'; // Throw could be better here though 
  }

  // any operation you need to do is here
  // if you need to sum number between start and end its called
  // For example summing operation
  return end > start 
           ? (end * (end + 1) / 2) - ((start - 1) * start / 2)
           : (start* (start + 1) / 2) - ((end- 1) * end / 2)
}

console.log(sumAll(10, 12));

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