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

[Isiah Meadows]

Most likely lack of interest and nobody trying to push it through the
process. It's come up repeatedly, but no one has actually tried to
write up a formal proposal and get someone on TC39 to champion it.
-----

Isiah Meadows
me at isiahmeadows.com


On Fri, Feb 24, 2017 at 8:28 AM, 段垚 <duanyao at ustc.edu> wrote:
>
> 在 2017/2/24 20:08, Claude Pache 写道:
>>>
>>> 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`.
>> ```
>>
>> In your JSON example:
>>
>> ```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
>
>
>
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