src: deprecate root and GLOBAL variables

[JacksonTian]

The root and GLOBAL never be documented.

[silverwind]

I think these should be pretty low risk to remove. If someone has an idea on how to print a deprecation warning when accessing the global or its properties, we could also go that route.

[Fishrock123]

If someone has an idea on how to print a deprecation warning when accessing the global or its properties

Use a Getter?

[brendanashworth]

There shouldn't be much code relying on this but there may be some so we do need a deprecation message.

edit: btw the commit log should be src: not lib:

[silverwind]

Use a Getter?

Won't work for usage like GLOBAL.setTimeout() is suppose.

[Fishrock123]

@silverwind isn't that still accessing GLOBAL from global?

[silverwind]

@Fishrock123 right, something like this should work:

Object.defineProperty(global, 'GLOBAL', {get: function() {
  util.deprecate(function() {}, "'GLOBAL' is deprecated, use 'global'");
  return global;
}});

@JacksonTian could you try incorporating such a print to both globals instead of removing them?

[silverwind]

Better one:

Object.defineProperty(global, 'GLOBAL', {
    get: util.deprecate(function() { return global; }, "'GLOBAL' is deprecated, use 'global'")
});

[targos]

maybe also make the property writable ?

[silverwind]

maybe also make the property writable ?

Right, this is getting interesting now. Below code should only print once on first read/write access:

var g = r = global;
var accessGlobal = util.deprecate(function(val) {
    if (val) g = val;
    return g;
}, "'GLOBAL' is deprecated, use 'global'");
var accessRoot = util.deprecate(function(val) {
    if (val) r = val;
    return r;
}, "'root' is deprecated, use 'global'");

Object.defineProperty(global, 'GLOBAL', {get: accessGlobal, set: accessGlobal});
Object.defineProperty(global, 'root', {get: accessRoot, set: accessRoot});

[silverwind]

One more revision:

const holders = {GLOBAL: global, root: global};
const accessGlobal = util.deprecate(function(val) {
    if (val) holders.GLOBAL = val;
    return holders.GLOBAL;
}, "'GLOBAL' is deprecated, use 'global'");
const accessRoot = util.deprecate(function(val) {
    if (val) holders.root = val;
    return holders.root;
}, "'root' is deprecated, use 'global'");

Object.defineProperty(global, 'GLOBAL', {get: accessGlobal, set: accessGlobal});
Object.defineProperty(global, 'root', {get: accessRoot, set: accessRoot});

@JacksonTian feel free to use something like that. Otherwise, I could do a PR that succeeds this one :)

[JacksonTian]

@silverwind The PR is updated, please review it again.

[bnoordhuis]

GLOBAL === global and root === global so you can just return this inside the setter, no need to create a separate object.

Apropos assignment, I'd replace the getter/setter inside the setter, e.g.:

Object.defineProperty(global, 'GLOBAL', {
  configurable: true,  // but not enumerable
  get: util.deprecate(function() { return this; },
                      `'GLOBAL' is deprecated, use 'global'`),
  set: function(value) {
    const desc = { configurable: true, enumerable: true, value: value };
    Object.defineProperty(this, 'GLOBAL', desc);
  },
});

Ditto for root. You can even go one step further and redefine the property inside the getter as well if you change it to:

get: util.deprecate(function() {
  const desc = { configurable: true, enumerable: true, value: this };
  Object.defineProperty(this, 'GLOBAL', desc);
  return this;
}, `'GLOBAL' is deprecated, use 'global'`)

That prints a warning on the first access and then gets out of the way. It won't regress code that uses GLOBAL or root in performance-sensitive code.

[silverwind]

+1 for using this.

@bnoordhuis I have a bit of a hard time understanding why running defineProperty each access can be faster, but you're probably right :)

[bnoordhuis]

@silverwind The getter calls defineProperty on the first access. After that the property is no longer a getter, just a regular property.

[silverwind]

@bnoordhuis oh right, thats quite genius!

[targos]

@bnoordhuis 👍 very clever

The setter can be simplified using shorthand property:

set(value) {
  const desc = { configurable: true, enumerable: true, value: value };
  Object.defineProperty(this, 'GLOBAL', desc);
}

[targos]

and maybe it should be writable: true as well ?

[bnoordhuis]

Good point, it should be writable when setting the value (but not when setting the getter/setter pair.)

[JacksonTian]

Hi everyone, I updated the PR by your comments, thanks.

[Fishrock123]

Should be Object.defineProperty(this, name, desc);

[cjihrig]

Tiny suggestion: the code might look a little better if you pulled the NativeModule.require('util') out into a variable. Feel free to ignore if you want.

[cjihrig]

LGTM with the same suggestions. And +1 to this being semver-major.

[ChALkeR]

GLOBAL[\.\[] grep: https://gist.github.com/ChALkeR/16d0fcd8ff17568a9747

[jasnell]

LGTM as semver-major

[silverwind]

ping @JacksonTian

[brendanashworth]

@bnoordhuis back then, root and GLOBAL were just outright removed, but when they were deprecated I changed it to semver-minor. +1 for major though.

[JacksonTian]

Updated. Thanks all.

[thefourtheye]

LGTM

[ChALkeR]

LGTM (if passes CI)

[silverwind]

CI: https://ci.nodejs.org/job/node-test-pull-request/1604/

[bnoordhuis]

Unrelated lint error addressed by #5161. Landed in 4e46931, thanks @JacksonTian!