The browser storage localStorage is not available. Either your browser does not support it or you have disabled it or the maximum memory size is exceeded. Without localStorage your solutions will not be stored.

# NaN

`NaN` is a value representing Not-A-Number. Numeric operations or functions return `NaN` if they cannot calculate a value. We had seen this with `parseInt`. It returns `NaN`, if it can't parse a number. Another example is the calculation of the square root from a negative number:
``````let age = parseInt('Babylon');
let length = Math.sqrt(-1);``````
Both `age` and `length` get the value `NaN`.

If you want to test for `NaN`, you unfortunately can't use strict equality. `NaN` is the only value in JavaScript that when compared to itself returns `false`. That is, `NaN === NaN` results in `false`. To check if a value is `NaN` use the `Number.isNaN` function:
``````let input = 'Babylon';
let message;
let age = parseInt(input);
if ( Number.isNaN(age) ) {
message = 'Input is not a number!';
}``````

## Exercise

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`.
Use a loop. Within the loop use `parseInt()`.
``````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;
}``````

loving