Cannot understand this javascript nan practice problem. Please help in explaining it.

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Javascript

Question:

Write a function parseFirstInt that takes a string and returns the first integer present in the string. If the string does not contain an integer, you should get NaN.

Example: parseFirstInt('No. 10') should return 10 and parseFirstInt('Babylon') should return NaN.


Explanation:

> we declare a function 'parseFirstInt'

> it has 1 parameter 'input'

> we declare a variable 'inputToParse'

> we initialize it with a value of the input string

> we use a 'for loop' to loop over the elements of the input string

> we then declare another variable inside the 'for loop' which is 'firstInt'

> we initialize its value with the output we get when we run the parseInt method on variable 'inputToParse' and store them in the firstInt variable

> we then open an if else statement

> our condition is plain & simple

> if value of 'firstInt' is NaN then we want it to exit the loop and return NaN

> if value of 'firstInt' is not NaN then we want it to execute the block of code in the if / else loop

> we keep checking for the first integer by using the loop

---------stopped understanding from here---------

What I have tried:

Answer:

function parseFirstInt(input) {
let inputToParse = input;
for (let i = 0; i < input.length; i++) {
let firstInt = parseInt(inputToParse);
if (!Number.isNaN(firstInt)) {
return firstInt;
}
inputToParse = inputToParse.substr(1);
}
return NaN;
};