Uglifier 3.1.0 produces "invalid assignment left-hand side"

[bodrovis]

Good day. After updating to Uglifier 3.1.0 I am starting to get a JS error in production saying "invalid assignment left-hand side". It happens on Heroku with Rails 5, Ruby 2.3. I am not really sure whether this should be reported here or at UglifyJS repo. After some inspection it appeared that the following line is problematic:

do 1 = 1, u /= 1, dt.style(t, e, u + a); while (1 = o() / s, !1)

This is a deobfuscated line of code that relates to jQuery 1 (it happens with jQuery 2 as well). Switching back to Uglifier 3.0.4 solves the problem. I can send minified and deobfuscated js files.

[jasonroelofs]

I have also run into this. The generated code is such:

for(var o="function"==typeof require&&require;0<r.length;0++)i(r[0]);return i}

That's a number zero getting an increment operator. Previously that was a proper variable s. I'm not really sure what underlying code is hitting this but it seems to be some shim code to loading compiled ES6 modules.

[lautis]

Does this happen if you disable reduce_vars and collapse_vars options? Those were enabled by default in 3.1 (and also UglifyJS2 2.8.0).

[vanitu]

+1 same issue. solved by downgrading to 3.0.4

[bodrovis]

@lautis sorry for a stupid question, but where should I provide these options for Rails?

[lautis]

@bodrovis, in config/application.rb: config.assets.js_compressor = Uglifier.new(compress: { reduce_vars: false, collapse_vars: false })

[brodjustice]

Not sure if this is the same issue but 3.1 breaks rails 3 by somehow messing up jquery. Fixed by going back to 3.0.4. I can dig in to provide more detail if required.

[jasonroelofs]

@lautis Thanks for the pointer. The problem occurs when reduce_vars: true. From my testing, collapse_vars does not trigger the problem.

[bodrovis]

Yeah, setting reduce_vars to false fixes it.

[ahorek]

minification of

function isAllChecked() { var boxes = $('body').find('input[type=checkbox]'); var all_checked = true; boxes.each(function(i) { if (!$(this).is(":checked")) { all_checked = false; } }); return all_checked; }

produces

function isAllChecked() { var c = $("body").find("input[type=checkbox]"); return c.each(function() { $(this).is(":checked") || (!0 = !1); }), !0; }

!0 = !1 => invalid assignment left-hand side

reduce_vars disabled

function isAllChecked() { var c = $("body").find("input[type=checkbox]"), e = !0; return c.each(function() { $(this).is(":checked") || (e = !1); }), e; }

[lautis]

Switched the default value to false for reduce_vars in 3.1.1.

[bodrovis]

@lautis Kiitos!

[ncuesta]

@lautis Thanks for your dedication! This bug just hit us and you shipped the fix before we could even determine the root cause.

Just stopped by to say you're awesome and, once again, thank you for your hard work.

[vanitu]

Thanks a lot for quick fix and support. Great!

[lautis]

There's a spec now that catches at least some errors like this in the future. I changed the minification test to use ExecJS.compile instead of UglifyJS to parse the output of minifying UglifyJS itself. I changed this to make the test suite a bit faster, but it also would've caught the error in 3.1.0.

https://github.com/lautis/uglifier/commit/c800c33daebadaf9ecd3562abc2b27e8279849d2