Interesting, it seems that the javascript runtime is smart enough detect this pattern and actually create a named function (I tried Chrome and Node.js)

    const foo = () => {}
    console.log( foo.name );

actually outputs 'foo', and not the empty string that I was expecting.

   const test = () => ( () => {} );
   const foo = test();
   console.log( foo.name );

outputs the empty string.

Is this behavior required by the standard ?

Yes, in great detail. https://tc39.es/ecma262/multipage/ordinary-and-exotic-object... is the specification, and for the TL;DR https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe... is pretty good.

You're probably remembering how it used to work. This is the example I remember from way back that we shouldn't use because (aside from being unnecessary and weird) this function wouldn't have a name in stack traces:

  var foo = function() {};

Except nowadays it too does have the name "foo".

But to call foo in bar you must define foo before bar.

function foo(){} is also callable if bar is defined before foo.

Not true at the top-level.

Not sure what you find not true about it. All named “function”s get hoisted just like “var”s, I use post-definitions of utility functions all the time in file scopes, function scopes, after return statements, everywhere. You’re probably thinking about

  const foo = function (){}

without its own name before (). These behave like expressions and cannot be hoisted.

> I use post-definitions of utility functions all the time in file scopes, function scopes, after return statements, everywhere

I haven't figured out if people consider this a best practice, but I love doing it. To me the list of called functions is a high-level explanation of the code, and listing all the definitions first just buries the high-level logic "below the fold". Immediately diving into function contents outside of their broader context is confusing to me.

I don’t monitor “best” practices, so beware. But in languages like C and Pascal I also had a habit of simply declaring all interfaces at the top and then grouping implementations reasonably. It also created a nice “index” of what’s in the file.

Hoisting also enables cross-imports without helper unit extraction headaches. Many hate js/ts at the “kids hate == and null” level but in reality these languages have a very practical design that wins so many rounds irl.

Does the function know it’s called foo for tracing/error logging/etc?

Not really, its an anonymous function stored in a variable foo