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 [email protected] On Fri, Feb 24, 2017 at 8:28 AM, 段垚 <[email protected]> wrote: > > 在 2017/2/24 20:08, Claude Pache 写道: >>> >>> 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. > > > 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 > > > > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
