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JavaScript JavaScript Basics (Retired) Creating Reusable Code with Functions Random Number Challenge, Part II Solution

Daniyar Basharov
Daniyar Basharov
2,957 Points

Why there is no ERROR message when I enter NaN as an argument like '100' insteat of 'hunred'

here is my code

function getRandomNumber(bottomNumber, topNumber) {
    var betweenRandomNumber = Math.floor( Math.random() * (topNumber - bottomNumber + 1)) + bottomNumber;
    if ( isNaN(bottomNumber) === true || isNaN(topNumber) === true ) {
            throw new Error("Some arguments are not a number");

    } else {
            return betweenRandomNumber;

console.log( getRandomNumber (10, 20) );
console.log( getRandomNumber (2, '100') );
console.log( getRandomNumber (100, 500) );
console.log( getRandomNumber ('200', 300) );
console.log( getRandomNumber (1000, 10000) );


Aaron Martone
Aaron Martone
3,290 Points

Because JS attempts to coerce your value to a data type depending on how you reference it. If you do '100' + 10, JS coerces the 10 number into a string and performs '100' + '10' resulting in '10010'. And '10010' is a String, despite it looking like a number to us. A String is NOT a NaN value. Try dividing 0/0, the result is NaN. So if you console.log( isNaN( 0/0 ) ); you get true. But if you log console.log(isNaN('10010')) you get false, because a String value (even though it looks numeric) is NOT a NaN value.

Mark Bacolcol
Mark Bacolcol
7,354 Points

@Aaron - A number within a string (isNaN("20")) runs false for me and the function returns an appropriate value. I tried using "20test" as a parameter and received an error as expected. So does JS treat strings with only numbers, as numbers?