deprecate --use_strict

[ljharb]

I'd like to reopen the discussion from nodejs/node-v0.x-archive#7479 if possible about somehow deprecating/removing this flag.

Whether the v8 team is willing to remove or rename it, or not (which we should probably re-investigate), I would like node to find a way to have it be removed or renamed.

[Fishrock123]

cc @nodejs/v8

[Fishrock123]

Arguments are passed verbatim to v8, I'm not sure we're keen on altering that..

[mscdex]

I'm -1 on interfering with (or documenting) command-line options provided by v8.

[vkurchatkin]

-1, this flag is useful

[Fishrock123]

-1, this flag is useful

@vkurchatkin Mind to elaborate on that?

[ljharb]

How is it useful? The flag is not the same as "use strict", and it's dangerous to execute sloppy code in strict mode anyways.

[cjihrig]

As recently as #6377, we rejected documenting V8 flags. This goes even further beyond that. I think it would be simplest for people to just not use it.

[ljharb]

The reasons for rejecting documentation is given as "… those are not under our control to change but as soon as we document it they become our responsibility to maintain". This is different - this is ensuring with certainty that no node users could ever depend on the v8 flag, which reduces the maintenance needed from the node core team (aside from maintaining a blacklist, for example)

[ljharb]

In other words, if --use_strict was removed by the v8 team, it's a breaking change for node anyways, documented or not. Blacklisting it lets you control when the breaking change occurs, and prevents it from ever occurring in the future.

[vkurchatkin]

Don't want to state the obvious, but it's useful when you want to run all javascript in strict mode. I think it's well understood that strict mode is not the default mode only because it's not backwards compatible.

[ljharb]

@vkurchatkin yes but --use_strict is not JavaScript, and at least in past versions of node, even some internal modules failed with this flag. If you want to run all of your JS in strict mode, you'd use ES6 modules (babel-transpiled, or one day, native) or put "use strict" on the top of every file - when would you want to run code you didn't author in a nonstandard mode?

[vkurchatkin]

I agree that most people don't need it, but that doesn't mean that we should remove it.

For example I use v8 on android to run some js in strict mode and use node to test this code on desktop. There are no dependencies, so I use --use_strict

[trevnorris]

@ljharb There are 389 options in node --v8-options, and I'm pretty sure ones like --use_strong, or --strong_this or --fast_math or --expose_wasm or --expose_gc or --allow_natives_syntax (all of these I do use in development), are "not JavaScript". This discussion revolves around an obscure flag, just like many others, that sit outside our direct control. It seems strange we'd consider removing only one of potentially many "not JavaScript" or not "useful" ones without taking into consideration all the other flags that should also be removed.

Also, what evidence is there that this flag is actually problematic or harmful in the ecosystem?