Any way to force strict mode in node?

Question

Could not find this answer anywhere, but I did find several mailing lists where this was discussed, these are rather old however and I have no idea if this is implemented or not.

Is there anyway to force using strict mode in node.js?

Writing "use strict"; in all my .js files... well, i prefer it being forced to using strict mode, rather than adding extra boilerplate.

I would highly suggest checking out [this much updated answer (rather than the dangerous answer which was chosen)](https://stackoverflow.com/a/51970329/124486) — Evan Carroll, Sep 07 '20 at 00:45

Chad Cache · Accepted Answer · 2016-11-16T07:48:32.703

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According to Lloyd you can now place

"use strict";

at the top of your file in node >= 0.10.7, but if you want your whole app to run in strict (including external modules) you can do this

node --use_strict

edited Nov 16 '16 at 07:48

answered Jan 07 '13 at 18:14

Chad Cache

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eek: fs.js:1497 function emit() { ^^^^^^^^ SyntaxError: In strict mode code, functions can only be declared at top level or immediately within another function. – j03m Jan 17 '13 at 19:53
one of the modules you're using is not following the strict rules – Chad Cache Jan 18 '13 at 19:30
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oh O_o, so you cant use the filesystem if you force strict? which version of node are you using, im not getting this on v0.8.12 – Chad Cache Jan 18 '13 at 22:38
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'v0.8.16' <--- hmm odd. Let me go verify. – j03m Jan 22 '13 at 16:36
01734a-j03m:node-limiter j03m$ node --use_strict test/exampleLimiter.js fs.js:1497 function emit() { ^^^^^^^^ [REDACTED] var vows = require('vows'), assert = require('assert'); var Limiter = require('../limiter.js'); var namespace = 'vowstest'; var mockUid = '1234556'; var Membase = require('memcached'); var m = new Membase("127.0.0.1:11211"); – j03m Jan 22 '13 at 16:38
that's of course using vows, assert and memcached, but it's definitely thrown in fs. – j03m Jan 22 '13 at 16:39
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In node v0.9.x and newer the `--use_strict` flag works as expected. – TooTallNate Feb 05 '13 at 05:52
in node v0.8 with `--use_strict` I got `ReferenceError: global is not defined` in `node.js` itself – vincentlcy Jun 09 '13 at 16:50
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Note that `--use_strict` will set strict mode to the whole application, include all exteneral modules, which are out of your controls. – Lewis Feb 05 '15 at 14:58

score 60 · Answer 2 · answered May 19 '13 at 09:36

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In node 0.10.7 you can enforce strict mode at file level by placing "use strict"; at the top of your file. Finally!

answered May 19 '13 at 09:36

Lloyd

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score 33 · Answer 3 · answered Aug 22 '18 at 15:33

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Just use "use strict"; at the top of applicable files. I know it's tempting to try to cut out boilerplate, but it simply can not be done in Javascript. The node flag which shall not be named^[1]

is undocumented, and unsupported by Node itself.
has faced proposals to remove it.
is node-specific and is not supported in any other JavaScript engine.
is unstandardized.
it is not the same as "use strict"; because it is a compiler global, and like all globals you're potentially adversely impacting someone else's code.
everything is subject to bugs. strict mode and sloppy-mode may be subject to different bugs. that is to say, some strict mode bugs are unique to strict mode

Some other programmers may think this is similar to -wALL or the like, it's not. This is standardized functionality that you're enabling in an ad-hoc fashion (breaking the standard) and changing everyone's compiler semantics.

Footnotes

The node flag is --use_strict. Don't use it.

answered Aug 22 '18 at 15:33

Evan Carroll

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Can you tell me where you found that it is "unsupported by Node?" Is that just inferred from the fact that it's not documented? – pushkin Mar 01 '19 at 20:26
Mostly. And because it's not a Node thing at all, it's a pass through to v8. – Evan Carroll Mar 01 '19 at 21:21
Thank you! I wondered why I couldn't find it in the [Node cli docs](https://nodejs.org/api/cli.html). – Galen Long May 18 '19 at 15:48
proposals to remove it was rejected/closed https://github.com/nodejs/node/issues/6429 – Michael Freidgeim Jan 02 '22 at 01:58

Gianluca Casati · Answer 4 · 2014-02-11T11:36:13.390

You can also use

https://npmjs.org/package/use-strict

that is, write once

require('use-strict')

or even take a step forward and use

https://npmjs.org/package/node-strict

Please note that use-strict will turn on strict more on every module required after invocation.

If you prefer a not invasive approach, I wrote another module

https://www.npmjs.org/package/strict-mode

which enables strict mode only in your package. I think that is more a "Do What I Mean" solution.

score 20 · Answer 5 · answered Mar 06 '13 at 15:19

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You can also provide the strict flag on the shebang interpreter directive.

#!/usr/bin/env node --use_strict

But currently (at least pre v0.9.x) it suffers the same problems described by the comments in @chad-scira's answer discuss.

answered Mar 06 '13 at 15:19

John Lehmann

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`env` doesn't allow you to pass parameters like that, does it? – Letharion Sep 17 '14 at 07:54
Works for me, on OSX 10.9.4. – John Lehmann Sep 18 '14 at 12:55
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yeah - still exemplifies a terrible enforced convention, that being two competing lines of code that have to be at the top of a file. – aaaaaa Jan 25 '15 at 04:58
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Beware, `env` will work with extra parameters like that on OSX, but not on Linux. – AerandiR Sep 13 '15 at 08:18

score 2 · Answer 6 · answered Jan 12 '21 at 16:30

It's worth noting that ESLint enforces strict mode by default. It won't stop you from running node on a file that doesn't adhere to strict mode of course, but if you have ESLint as a required part of your build and CI process, then developers will only be able to commit strict-mode code.

score 1 · Answer 7 · answered Aug 09 '23 at 11:22

If you're using CommonJS (NodeJS uses CommonJS modularization by default) there's no strict mode unless you include "use strict" in the file or execute node with the --use_strict flag

But in ECMAScript modules, strict mode is by default. You can enable it adding "type": "module" to package.json

Any way to force strict mode in node?

7 Answers7

Footnotes

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