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

Ron Buckton Ron.Buckton at microsoft.com
Sun Aug 9 03:12:28 UTC 2015

One of the main purposes of the `nameof` operator is to provide the string value of a symbol, so that if you perform a "Rename" refactoring of that symbol that the change is also reflected. This is primarily for cases where you perform precondition assertions tied to an argument:

  static void Method(string x) {
    if (x == null) throw new ArgumentNullException(nameof(x));

Now, if I later rename `x`, I don't need to also find any string literals of "x" and manually update them.

There are other uses of `nameof`, but they all boil down to roughly the same thing.

From: Isiah Meadows<mailto:isiahmeadows at gmail.com>
Sent: ‎8/‎8/‎2015 7:23 PM
To: Behrang Saeedzadeh<mailto:behrangsa at gmail.com>; EcmaScript Discuss Mailing List<mailto:es-discuss at mozilla.org>
Subject: Re: What do you think about a C# 6 like nameof() expression for JavaScript.

Call me crazy, but I don't see anything that couldn't be done more concisely with a string literal. Is it supposed to be able to do this?

function foo(x) {
  return nameof(x);

foo(bar); // "bar";

In that case, the engine would have to keep track of usages as well, in a similar sense as `arguments.callee`, and if it were a function, it would make optimization quite difficult, as engines don't have the capacity to statically analyze that such a function is used.

If it is like `typeof`, we now have a breaking change - a keyword that was a valid Identifier before.

// Error?
function nameof(value) {
  return value.name<https://na01.safelinks.protection.outlook.com/?url=http%3a%2f%2fvalue.name&data=01%7c01%7cron.buckton%40microsoft.com%7ca2e2c4d35400435810d008d2a061897d%7c72f988bf86f141af91ab2d7cd011db47%7c1&sdata=pwV45avF9RX6COETpoLIY4EF%2bmCVmk6kEEmLc2JXSCY%3d>;

var bar = {name: 2};
nameof(bar); // "bar" or 2?

I don't think this is going to work out in practice, not in ECMAScript proper. You might appreciate Sweet.js, though.

On Sat, Aug 8, 2015, 21:27 Behrang Saeedzadeh <behrangsa at gmail.com<mailto:behrangsa at gmail.com>> wrote:
Forgot to mention that nameof works with local variables too:

function foo() {
 var aNum = 1;
 console.log(nameof(aNmum), aNum);

On Sat, Aug 8, 2015 at 10:38 AM Behrang Saeedzadeh <behrangsa at gmail.com<mailto:behrangsa at gmail.com>> wrote:

So basically we could use it like this:

function aFunc(aParam) {
    throw new Error(nameof(aParam));

and nameof(aParam) would return the string "aParam".

This is possible to do even right now using arguments.callee and some hacky code, but having it built-in to spec would be nicer IMHO.

Best regards,
Behrang Saeedzadeh
Best regards,
Behrang Saeedzadeh
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