CODEWITHSUNDEEP
javascript
Richard
Richard

Reputation: 65510

JavaScript: convert string/number to a number or null, return 0 for 0?

In my JavaScript I currently have this nice expression:

var b = {
   items: +a || null
};

This sets b.items to a Number if a is a String, or a Number greater than 0, and as null if a is null/undefined.

However, it also returns null if a is 0. Now I'd like to change it so that it returns 0 if a is 0. (This seems like the right way to handle real data: if it's zero, we want to know that it's zero, and if it doesn't exist, we want to know that too.)

I've looked at this question and tried these two: 

items: 1/a ? +a: null
items: isNaN(a) ? null : +a

but these both return 0 if a is null. They should return null.

Is there a way I can return 0 if a is 0, and null if it's undefined?

Update: Here's a summary of everything the expression needs to do:

"72" -> 72
"0" -> 0
1 -> 1
0 -> 0
null -> null
undefined -> null

Upvotes: 2

Views: 827

Answers (4)

r0hitsharma
r0hitsharma

Reputation: 1762

This should work as well:

var b = {
   items: a != null? +a : null
};

Based on https://stackoverflow.com/a/15992131/1494833

Upvotes: 0

Tushar
Tushar

Reputation: 87203

You can check the type of a in ternary operator.

var b = {
    items: typeof (+a) == 'number' ? +a : null
};

Demo:

var b = {
  items: typeof (+"0") == 'number' ? +"0" : null
};


alert(b.items);

EDIT

Hack to check null.

function f(a) {
  return isNaN('' + a) ? null : parseFloat(a)
}


alert(f(0));
alert(f(null));
alert(f(undefined));

Upvotes: 1

Sky Fang
Sky Fang

Reputation: 1101

Try this

var b = {
   items: +a ||(a==0?0:null)
};

Upvotes: 0

hair raisin
hair raisin

Reputation: 2628

You could specifically test for null and undefined

var b = {
    items: ('undefined' === typeof a || null === a) ? null : +a
};

Upvotes: 1

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