Javascript Practice 73: JS Hero - NaN

 

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.

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;

};

> 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

> for eg lets say our 'inputToParse' is 'Javascript 101'

> so parseInt will give us a NaN output

> this will be stored in firstInt variable

> we then open an ' if ' statement to check if firstInt is ' NaN ' or ' not NaN '

> if it is NaN then the code inside the block of ' if ' statement does not run

> instead we apply the substr(1) method which returns a portion of the string from the index 1 and extending up to the last index.

> so the new 'inputToParse' value shall be ' avascript 101'

> this value will get stored in the 'firstInt' variable and again the condition in the ' if ' statement will be checked 

> this process will keep on repeating itself till the loop stopping condition is met

> if we encounter any numbers then they get stored in the 'firstInt' variable

> if there are no occurrences of numbers then we will have nothing stored in the variable 'firstInt' 

> the stopping condition is met once we run out of characters in 'inputToParse' variable

> so if we do have numbers then the function will return the integer

> if the stopping condition is met and we do not find any integers then we shall be returned NaN