static/class properties

Erik Arvidsson erik.arvidsson at gmail.com
Thu Sep 19 06:43:09 PDT 2013


On Thu, Sep 19, 2013 at 9:30 AM, Rick Waldron <waldron.rick at gmail.com> wrote:
> On Thu, Sep 19, 2013 at 4:16 AM, Dmitry Soshnikov
> <dmitry.soshnikov at gmail.com> wrote:
>>
>> Hi,
>>
>> Out of curiosity: we have static methods, but seems there is no yet
>> ability to define a class/static property/constant.
>>
>> class A {
>>   const VALUE = 10;
>> }
>>
>> or (probably better to be consistent with static methods):
>>
>> class A {
>>   static VALUE = 10;
>> }
>>
>
> There are a few reasons, the first being that there was no "static" prefix
> when maximally minimal classes were accepted, but of course the class
> feature grew a little (which is a good thing). "static", with regard to
> methods, is straight forward, whereas data properties create a potential
> ambiguity:
>
> class A {
>   const VALUE = 10;
> }
>
> A decision would have to be made for "const VALUE = 10" here: does it mean
> mean `A.VALUE` and not `var a = new A(); a.VALUE;`? If it means the latter,
> then there are implications that will change a possible future that includes
> "private x = 1" in the same class-body position.
>
> I spoke with Allen off-line and he reminded me that a static "const-like"
> could be created like this:
>
> class A {
>   static get VALUE() { return "some constant value"; }
> }
>
> A.VALUE;
>
> (I quoted const-like, because this is still configurable)
>
>
>
>>
>> Was it a special reason or was it just forgotten? (One could define a var
>> in the static scope, but seems it's useful to have the feature inline in the
>> class bodies).
>>
>> P.S.: in addition -- why not to reuse `static` for also simple functions?
>>
>> function getHeavyValue() {
>>   static heavyValue;
>>   if (!heavyValue) {
>>     // heavy calc
>>   }
>>   return heavyValue;
>> }
>>
>
> This is a no-go because "static" is only reserved in strict mode, which
> means
>
> function foo() {
>   static = 1;
> }
>
> (awful, yes—but legal)

Not true. static is a keyword since ES2.

7.4.3, Future keywords

http://www.ecma-international.org/publications/files/ECMA-ST-ARCH/ECMA-262,%202nd%20edition,%20August%201998.pdf

-- 
erik


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