What do you think about a C# 6 like nameof() expression for

Ron Buckton Ron.Buckton at microsoft.com
Fri Jun 14 18:51:09 UTC 2019


Since `nameof` does not actually evaluate anything, the following would be legal:

```
const x = nameof y; // "y"
const y = 1;
```

However, the shorthand property name workaround is not legal due to TDZ:

```
const x = Object.keys({y})[0]; // error due to TDZ
const y = 1;
```

With the shortand property name workaround you also run into the added runtime overhead of:

  *   Constructing an object (`{y}`)
  *   Looking up a property (`Object.keys`)
  *   Calling a function (`Object.keys`)
  *   Allocating an array
  *   Indexing into the array

Whereas `nameof` has *no* runtime overhead, because it would be handled during static semantics.


From: es-discuss <es-discuss-bounces at mozilla.org> On Behalf Of guest271314
Sent: Friday, June 14, 2019 11:17 AM
To: Stas Berkov <stas.berkov at gmail.com>
Cc: es-discuss at mozilla.org
Subject: Re: Re: What do you think about a C# 6 like nameof() expression for

Terms such as "more robust", "Less fragile." , "Less mess." are subjective. "Fragile" how? What is meant by "mess"?

If the proposal is that ```nameof``` is briefer than using shorthand property names or computed property names to get an identifier as a string, then ```nameof``` would be less code.

> You can rename field/property without fear you break something (using IDE refactoring tools).

The use case appears to be within the context of an IDE?

For users that roll their own code by hand at a text editor and do not use an IDE for composing code (or relying on an IDE for logging errors), am not able to discern how ```nameof``` is different than using ```Object.getOwnPropertyDescriptors(other).name.value``` or ```Object.keys({userName})[0]```. The actual code will need to be tested in different browsers anyway before deployment to get the actual results.

If a user has decided they _have_ to use some form of a dynamic "IDE" to compose code and log errors - while they are writing the code, they can open DevTools at Chromium or Chrome then select ```Sources``` => ```Snippets``` => ```New snippet```, where

```
const n = 123;
const n = 456;
```

will highlight the line where the error occurs - during writing the code - the as a red circle with a transparent "x" in the middle

```Uncaught SyntaxError: Identifier 'n' has already been declared````

To run the code press ```ctrl+enter```.




On Fri, Jun 14, 2019 at 5:48 PM Stas Berkov <stas.berkov at gmail.com<mailto:stas.berkov at gmail.com>> wrote:
Less fragile. Less mess. You can rename field/property without fear you break something (using IDE refactoring tools).
With high probablity you will break something when you refactor and have fields hardcoded as strings.
Someone can object that you can rename strings as well.
Issue here that you can ocassionally change non-related strings that should not be changed even they match or have matching substring.

On Fri, Jun 14, 2019 at 9:38 PM guest271314 <guest271314 at gmail.com<mailto:guest271314 at gmail.com>> wrote:
Is Case 1 equivalent to a briefer version of

```
   if (userName == undefined) {
       throw new Error(`Argument cannot be null: ${Object.keys({userName})[0]}`);
   }
```

?

If not, how is ```nameof``` different?

What is the difference between the use of ```message.hasOwnProperty(property)``` and ```nameof msg.expiration_utc_time```?

> You get more robust code.

How is "robust" objectively determined?




On Fri, Jun 14, 2019 at 5:21 PM Stas Berkov <stas.berkov at gmail.com<mailto:stas.berkov at gmail.com>> wrote:
ES can befit from `nameof` feature the same way as TS. There is no TS specific in it.
It was ask to introduce in TS as a workaround since TS is considered as extention of ES.

Case 1. Function guard.
```
function func1(param1, param2, param3, userName, param4, param5) {
   if (userName == undefined) {
       throw new ArgumentNullError(nameof userName); // `ArgumentNullError` is a custom error, derived from `Error`, composes error message like "Argument cannot be null: userName".
   }
}
```

Case 2. Access extended information an object property.
Assume a function
```
function protoPropertyIsSet(message, property) {
    return message != null && message.hasOwnProperty(property);
}
```
Then in code you use it as `if (protoPropertyIsSet(msg, "expiration_utc_time")) {... }`.
Having `nameof` would allow you to do that `if (protoPropertyIsSet(msg, nameof msg.expiration_utc_time)) {... }`.
You get more robust code.

On Fri, Jun 14, 2019 at 5:46 PM Augusto Moura <augusto.borgesm at gmail.com<mailto:augusto.borgesm at gmail.com>> wrote:
Can you list the benefits of having this operators? Maybe with example use cases

If I understand it correctly, the operator fits better in compiled
(and typed) languages, most of the use cases don't apply to dynamic
Javascript
The only legit use case I can think of is helping refactor tools to
rename properties (but even mismatch errors between strings and
properties names can be caught in compile time using modern
Typescript)

Em sex, 14 de jun de 2019 às 10:05, Stas Berkov
<stas.berkov at gmail.com<mailto:stas.berkov at gmail.com>> escreveu:
>
> Can we revisit this issue?
>
>
> In C# there is `nameof`, in Swift you can do the same by calling
>
> ```
>
> let keyPath = \Person.mother.firstName
>
> NSPredicate(format: "%K == %@", keyPath, "Andrew")
>
> ```
>
> Let's introduce `nameof` in ES, please.
>
>
> Devs from TypeScript don't want to introduce this feature in TypeScript unless it is available in ES ( https://github.com/microsoft/TypeScript/issues/1579<https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fmicrosoft%2FTypeScript%2Fissues%2F1579&data=02%7C01%7Cron.buckton%40microsoft.com%7C9b2c54f48f5d4505fb1008d6f0f494c9%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636961330684601102&sdata=P7VAkHGEM1WeVpzpovf9TxXOdkzcuQgcBsoGwMNqmuA%3D&reserved=0> )
>
> This feature is eagarly being asked by TypeScript community.
>
>
> I understand there are couple issues related to `nameof` feature in ES. They are: minification and what to do if user already has `nameof` function.
>
>
> Minification.
>
> 1. If your code to be minimized be prepared that variable names will also change.
>
> 2. (just a possibility) Minimizer can have option to replace `nameof(someVar)` with result of `nameof` function.
>
>
>
> What if user already has `nameof` function.
>
> 1. To maintain status quo we can user `nameof` function having priority over newly introduced language feature.
>
> 2. OR we can use `typeof` syntax, e.g. `nameof msg.userName` (// returns "userName" string)
>
> _______________________________________________
> es-discuss mailing list
> es-discuss at mozilla.org<mailto:es-discuss at mozilla.org>
> https://mail.mozilla.org/listinfo/es-discuss<https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fmail.mozilla.org%2Flistinfo%2Fes-discuss&data=02%7C01%7Cron.buckton%40microsoft.com%7C9b2c54f48f5d4505fb1008d6f0f494c9%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636961330684611108&sdata=hyL72vBqg5ecV6O%2BO33sWVN%2BQ2SOqeFyHGGKSw%2BH5fk%3D&reserved=0>



--
Atenciosamente,

Augusto Borges de Moura
_______________________________________________
es-discuss mailing list
es-discuss at mozilla.org<mailto:es-discuss at mozilla.org>
https://mail.mozilla.org/listinfo/es-discuss<https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fmail.mozilla.org%2Flistinfo%2Fes-discuss&data=02%7C01%7Cron.buckton%40microsoft.com%7C9b2c54f48f5d4505fb1008d6f0f494c9%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636961330684611108&sdata=hyL72vBqg5ecV6O%2BO33sWVN%2BQ2SOqeFyHGGKSw%2BH5fk%3D&reserved=0>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.mozilla.org/pipermail/es-discuss/attachments/20190614/450869ab/attachment-0001.html>


More information about the es-discuss mailing list