Confused about the NaN using isNaN() as condition please take a look on my code

function addStrNums(num1, num2) {
	// write your code here
let parsed1 = parseInt(num1);
  let parsed2 = parseInt(num2);

  if (isNaN(parsed1) || isNaN(parsed2) ) { return -1; }
   return parsed1 + parsed2;
console.log(addStrNums('2k', 'd3d'))
                        // 2     NaN   why  '2k' is an integer here and in the second is a NaN?
console.log(addStrNums('k2', '3d'))
                       //NaN     3

I don’t understand what you are asking. Can you please explain more?

ty for editing my post and sorry for the mess! what am asking about is what make the inputs in the first line considered as NaN and in the second not considered as NaN ; “2k” in the first is converted to an integer but in the second line is NaN

Look at what parseInt does with a string that starts with a number:

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ty this is exactly what i need to read to understand this topic!

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There are some confusing little corners like this all over Javascript. MDN does a pretty good job providing examples and discussion.

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