Add indent option to util.inspect?

[gla5001]

• Version: master
• Platform: all
• Subsystem: util

It was mentioned in comment on PR, that it might useful to have 'real indenting' for util.inspect via a new option passed in. This is to make it function more like JSON.stringify with passing in a space specifier. Is this something that people would like to see? Would it be useful?

Refs: #14545

[benjamingr]

I'd like to get feedback from some of the heaviest users of util.inspect (mainly logging libraries) on this.

I'm personally +1.

[silverwind]

One question is how the interaction of breakLength and the hypothetical indent should be. Should it still break off lines when indentation is enabled, possibly destroying the formatting?

[refack]

how the interaction with breakLength and the hypothetical indent should be

🤔
I can't think of an obvious way it will interfere... seems to me that is we simply add \n after {/[ and before }/] it becomes similar to emca262 compliant.

> console.log(util.inspect(o, {breakLength:4}))
{ a: 1,
  b: 2,
  c: 3,
  d: 4,
  e:
   [ 1,
     2,
     3,
     4,
     { f: 6,
       g: [Array] } ] }

If anyone can find an example case IMHO it should also go into the current tests.

[refack: edited claim for spec compliance]

[silverwind]

I can't think of an obvious way

Looks like I actually misinterpreted the breakLength description. There should actually be no issue, as indent should always "break" objects anyways effectively working like breakLength of 0.

[refack]

ping @domenic, you had reservations to share?

[domenic]

I don't see the motivation for this. Despite claims above, this has nothing to do with spec compliance. This is just someone's subjective formatting preferences. The name "indent" is especially bad; the lines are already indented. This is actually about inserting newlines (again, at a place that one contributor thinks looks nicer).

I don't think util.format should be a general-purpose formatting with additional options for everyone's aesthetic preferences. I think that's better left to libraries. The existing formatter is a great balance of readability and conciseness.

[refack]

@domenic I see your point. And I don't claim that this will make anything "up to spec" but the current implementation of the breakLength algorithm was also an arbitrary implementation - de15214#diff-38d4e5ad222633775fc89be4caa69a09R162, and I'd rather we give the users an option to indent in a way that is similar to JSON.stringify which is up to spec.

P.S. we're talking about util.inspect, not util.format, hence this should not affect console.log.

[gla5001]

agree that 'indent' is not the best name for the option if we choose to move forward with this. Maybe something like prettyFormat or something

[gla5001]

So this discussion has been pretty quiet for several days, how do I know if its worth working on or not?

[silverwind]

I'd interpret the current responses as being not enough to warrant an implementation. Let's give it a bit more time and otherwise close it.

[TimothyGu]

As others have articulated, util.inspect() is already an opinionated function. More "styles" of inspection belongs in a user module, not in util.inspect(). However, I do think an API to change the number of spaces used / the indentation character sounds like a fine idea, but implementation-wise it might not be as simple as one would think it is.

1. Format. We currently have a somewhat odd (but concise) indentation scheme for arrays. Note how there's only one space before [:

   { a: 1,
     d: 4,
     e:
      [ 1,
        2,
        3,
        4,
        { f: 6,
          g: [Array] } ] }

   It would be impossible to replicate this with tab delimiter, and it wouldn't look as good with non-2-space indentations:

   {   a: 1,
       d: 4,
       e:
        [   1,
            2,
            3,
            4,
            {   f: 6,
                g: [Array]   }   ]   }
   // lmao

2. Custom inspection. Currently indentation is handled in the custom inspection function (if one is provided). E.g. the one for URLSearchParams:

   node/lib/internal/url.js

   Line 190 in ab2b331

   return `${this.constructor.name} {\n ${output.join(',\n ')} }`;

   which provides the following fairly attractive output:

   URLSearchParams {
     'key' => 'value',
     'key' => 'value',
     'key' => 'value',
     'key' => 'value',
     'key' => 'value',
     'key' => 'value',
     'key' => 'value',
     'key' => 'value',
     'key' => 'value',
     'key' => 'value' }

   It would introduce much churn if we were to support changing indentation as the styles wouldn't match with existing code written to conform to our current style.

So for these reasons, I'm leaning towards closing this ticket as well.

[refack]

Can anyone see a path forward? We have a opinionated implementation (breakLength) but there is a more standardized format (JSON.stringify(obj, null, 2)).

1. Should we try to deprecate breakLength?
2. change it in a semver-major fashion?

BTW: AFAICT

node/lib/internal/url.js

Lines 189 to 191 in ab2b331

	if (length > ctx.breakLength) {
	return `${this.constructor.name} {\n ${output.join(',\n ')} }`;
	} else if (output.length) {

is the only custom inspection that supports breakLength (https://github.com/nodejs/node/search?utf8=%E2%9C%93&q=breakLength&type=)