how do I convert a string to int in JS, while properly handling error cases?
I want NaN returned when the argument is not really an integer quanityt:
- blank string should return NaN (not 0)
- mixed strings (e.g. "3b") should return NaN (not 3)
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5 Answers
function cNum(param) { return param === "" ? NaN : Number(param) } cNum(""); //returns NaN cNum("3b"); //returns NaN cNum("4.5"); //returns 4.5 
1 Comment
hammer
you may also check null as it will be treated as 0.
3 Comments
gap
I think, based on other SO Q&A, that parseInt will return "3" when given "3b" and "0" when given "".
Lightness Races in Orbit
Don't link to w3schools please. It's widely regarded as a poor and inaccurate reference.
Brian L
Really? I'll admit I don't do much web development, but I've never run across anything inaccurate there. Do you have an example?
function stringToInt(str) { var num = parseInt(str); if (num == str) return num; return NaN; } Examples
stringToInt("") NaN stringToInt("3") 3 stringToInt("3x") Nan 
1 Comment
gap
Simple, easy... I like it! Nothing built in though, huh?
var intval = /^\d+$/.test( strval ) ? parseInt( strval ) : NaN; 
Comments
You don't need much- if s is a string:
s%1 will return 0 if s is an integer.
It will return a non-zero number if s is a non-integer number,
and NaN if s is not a number at all.
function isInt(s){ return (s%1===0)? Number(s):NaN; } But although the number returned is an integer, to javascript it is still just a number.
