Convert NaN to 0 in javascript

You can do this:

a = a || 0

...which will convert a from any "falsey" value to 0.

The "falsey" values are:

• false
• null
• undefined
• 0
• "" ^{( empty string )}
• NaN ^{( Not a Number )}

Or this if you prefer:

a = a ? a : 0;

...which will have the same effect as above.

If the intent was to test for more than just NaN, then you can do the same, but do a toNumber conversion first.

a = +a || 0

This uses the unary + operator to try to convert a to a number. This has the added benefit of converting things like numeric strings '123' to a number.

The only unexpected thing may be if someone passes an Array that can successfully be converted to a number:

+['123']  // 123

Here we have an Array that has a single member that is a numeric string. It will be successfully converted to a number.

Using a double-tilde (double bitwise NOT) - ~~ - does some interesting things in JavaScript. For instance you can use it instead of Math.floor or even as an alternative to parseInt("123", 10)! It's been discussed a lot over the web, so I won't go in why it works here, but if you're interested: What is the "double tilde" (~~) operator in JavaScript?

We can exploit this property of a double-tilde to convert NaN to a number, and happily that number is zero!

console.log(~~NaN); // 0

Write your own method, and use it everywhere you want a number value:

function getNum(val) {
   if (isNaN(val)) {
     return 0;
   }
   return val;
}