`$inspect(...).with(...)`

[Rich-Harris]

Describe the problem

Some feedback we've had on $inspect is that this...

console.log('>>> HERE', foo, bar, baz);

...is a common pattern that doesn't work with $inspect, as it only takes a single value argument (in order to prevent ambiguity when providing a callback function).

Describe the proposed solution

@dummdidumm had a great idea — allow an arbitrary number of arguments, and put the callback in a .with method:

// these are effectively identical
$inspect('>>> HERE', foo, bar, baz);
$inspect('>>> HERE', foo, bar, baz).with(console.log);

// can also use `console.trace` or `debugger`...
$inspect('>>> HERE', foo, bar, baz).with(console.trace);

$inspect('>>> HERE', foo, bar, baz).with((type, ...values) => {
  debugger;
});

// ...or whatever custom logic you want to provide
$inspect('>>> HERE', foo, bar, baz).with((type, ...values) => {
  klaxon.play();
});

Alternatives considered

n/a

Importance

nice to have

[dooshiifox]

I don't think the way this feature is currently planned is great from a developer point-of-view. As a user of Svelte, I understand that these are macros and so can do whatever the hell they want, but they still look and feel like they should abide by how JavaScript works. As such, having the functionality of $inspect change depending on whether theres a method on the end feels... wrong. Perhaps something like $inspect.many(['>>> HERE', foo, bar, baz], (type, ...values) => { debugger; }) and keeping the current behaviour of $inspect?
That being said, the idea is useful, and I'll be happy to see it implemented either way.

[Not-Jayden]

// these are effectively identical
$inspect('>>> HERE', foo, bar, baz);
$inspect('>>> HERE', foo, bar, baz).with(console.log);

Can you clarify with these two cases. Is the expectation that they would actually be identical, or would the first one omit the type that's included in the .with() callback?
i.e.

$inspect('>>> HERE', foo, bar, baz); // Output: '>>> HERE foo bar baz'
$inspect('>>> HERE', foo, bar, baz).with(console.log); // Output: 'init >>> HERE foo bar baz'

That would be my expected/preferred behaviour, but maybe that could be considered confusing.

[Not-Jayden]

Perhaps .with() could have an optional includeType second config argument.

e.g.

$inspect('>>> HERE', foo, bar, baz).with(console.log, true); // Output: 'init >>> HERE foo bar baz'
$inspect('>>> HERE', foo, bar, baz).with(console.log, false); // Output: '>>> HERE foo bar baz'

Whether it should default to true or false I'm not too sure, though I'd probably lean towards false to make the example mentioned actually identical.

Also questionable if it should be a config object rather than a simple boolean for easier extensibility in the future 🤷‍♂️

Typescript example