# Proposal: a more consistent and stricter number converting function - Number.of()

Fri Feb 24 13:28:15 UTC 2017

>> Le 24 févr. 2017 à 04:50, 段垚 <duanyao at ustc.edu> a écrit :
>>
>> Hi,
>>
>>
>> Converting an arbitray value to a number in JS can be rather inconsistent and unexpected:
>>
>> * `null` and `undefined` are different: `+null === 0` but `+undefined` is NaN.
>>
>> * Empty string and non-nubmeric strings are different: `+"" === 0` but `+"foo"` is NaN.
>>
>>
>> This problem can be worse because JSON only support finite numbers:
>>
>> ```
>>
>> var total = 0;
>>
>> total += JSON.parse(JSON.stringify({ "value": 0/0 })).value;
>>
>> total === 0; //Oops, NaN is serialized as null, and then converted to 0
>>
>> ```
>>
>> So I propose a more consistent and stricter number converting function: `Number.of(value)`:
>>
>> 1. If `value` is `null` or `undefined`, return `NaN`;
>>
>> 2. If `value` is a number, return `value` itself;
>>
>> 3. If `value.valueOf()` returns a number, return that number, otherwise return `NaN`.
>>
>>
>> This means all non-number values except those have number type `.valueOf()` would be converted to NaN:
>>
>>
>> ```
>>
>> Number.of(null); // NaN
>>
>> Number.of(''); //NaN
>>
>> Number.of('1'); //NaN
>>
>>
>> var total = 0;
>>
>> total += Number.of(JSON.parse(JSON.stringify({ "value": 0/0 })).value);
>>
>> total; // NaN
>>
>> ```
>>
>>
>> What do you think?
>>
>>
>> Regards,
>>
>> Duan, Yao
>>
>
> Depending on the concrete situation, you might not need yet another way to convert into number.
>
> * If you know that your input is either a string or null/undefined (e.g., as the result of  `someHTMLElement.getAttribute('foo')`), you could use `Number.parseFloat()`, which will produce NaN for the empty string, null and undefined.

What I actually want is a function/operator that protect against
non-number values, including strings that can be parsed as numbers,
and objects whose `.toString()` happen to return strings can be parsed
as numbers.

>
> * If your issue is precisely with null/undefined, as it is the case in your JSON example, a more generic solution would be the null-coalescing operator `??`, which allows to express more precisely and more clearly what you mean. The semantics is:
>
> ```js
> a ?? b // evaluates `a`. If `a` is null or undefined, evaluates `b`.
> ```
>
>
> ```js
> var total = 0;
>
> total += JSON.parse(JSON.stringify({ "value": 0/0 })).value ?? NaN;
>
> Number.isNaN(total); // true. Hurray!
> ```

The null-coalescing operator `??` is awosome and will solve my null/undefined issue.
However, it seems there is little progress since it was proposed ( https://esdiscuss.org/topic/proposal-for-a-null-coalescing-operator ).
Are there objections or simply lack of interest?

>
> —Claude