javascriptparseint

Why does parseInt(string@2019) return NaN in JavaScript?

I am new to JavaScript and currently understand two things about the parseInt() method:

parseInt("100") // gives 100
parseInt("2019@string") // gives 2019

However, why would parseInt("string@2019") give NaN?

Solution

  • You can see the issue if you look at the W3Schools page for parseInt:

    If the first character cannot be converted to a number, parseInt() returns NaN.

    This is why the following returns NaN:

    console.log(parseInt("O123"));

    But if you have multiple numbers in a string, separated by a non-digit character, then it will not error - it'll just return the first number:

    Only the first number in the string is returned!

    console.log(parseInt("12b34"));

    This information is also found in the MDN page for parseInt:

    If the first character cannot be converted to a number, NaN is returned.