How do I convert a string to an int in Javascript?

Question

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)

Answer 1

function cNum(param) {
 return param === "" ? NaN : Number(param)
}
cNum(""); //returns NaN
cNum("3b"); //returns NaN
cNum("4.5"); //returns 4.5

• hammer: you may also check null as it will be treated as 0.

Answer 2

http://www.w3schools.com/jsref/jsref_parseInt.asp

• 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?

Answer 3

function stringToInt(str) {
 var num = parseInt(str);
 if (num == str)
 return num;
 return NaN;
}

Examples

stringToInt("")
NaN
stringToInt("3")
3
stringToInt("3x")
Nan

• gap: Simple, easy... I like it! Nothing built in though, huh?

Answer 4

var intval = /^\d+$/.test( strval ) ? parseInt( strval ) : NaN;

Answer 5

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.