> Le 24 févr. 2017 à 04:50, 段垚 <[email protected]> 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.
* 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!
```
—Claude
_______________________________________________
es-discuss mailing list
[email protected]
https://mail.mozilla.org/listinfo/es-discuss
