some es6 features are not understood by grunt uglify js?

Question

I used grunt-uglify in my project and I'm working with es6. for some es6 features, such as fat arrow function, it's throwing an error. I think the uglify don't understant that syntax. so do i have a way to fix this issue. I mean can i use anything to make uglify understand all the es6 syntaxes?

Yevhenii Bahmutskyi · Answer 1 · 2017-09-20T08:42:22.967

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You can use the harmony branch of grunt-contrib-uglify.

npm install git://github.com/gruntjs/grunt-contrib-uglify.git#harmony --save-dev

works perfectly with es6. No additional settings for grunt are required.

edited Sep 20 '17 at 08:42

answered Jul 03 '17 at 13:48

Yevhenii Bahmutskyi

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This was the only one that worked for me, but it did only after adding `grunt.loadNpmTasks('grunt-contrib-uglify-es');` this javascript line in the Gruntfile, as stated in the [official GitHub page](https://github.com/gruntjs/grunt-contrib-uglify/tree/harmony#grunt-contrib-uglify-es-v330--). – Harshith Rai May 13 '19 at 06:09
grunt-contrib-uglify.git#harmony is now deprecated – migli Dec 13 '19 at 07:36

Carlos Delgado · Accepted Answer · 2017-03-24T12:51:33.520

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Officially there's no tool that minifies ES6 yet (Other tools like Google Closure compiler supports ES6 but it transpile it into "traditional js" and then it's minified).

Although not all the es6 features are supported in UglifyJs, the Harmony branch of UglifyJS2 seems to support arrow functions and other features.

You can read the discussion about it in the issue of github here. It seems there's not another option to wait (or create your own ES6 minifier).

Update

Now you have 2 options to minify ES6:

edited Mar 24 '17 at 12:51

answered Jul 18 '16 at 07:04

Carlos Delgado

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Any news about that ? – NeoPix Mar 24 '17 at 16:47
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Bump! 2019 now.. Still facing uglify not being able to accept "let". – Dropout Dec 16 '19 at 14:55
2021 now and it is partly implemented. There is no support for .? operator but I havent discovered other problems yet... – Esteban Apr 02 '21 at 19:17
Also * of generator functions seems not to be understood yet. – aderchox Aug 14 '21 at 12:28

score 4 · Answer 3 · answered Dec 13 '19 at 08:38

A Grunt plugin ES6 parser, mangler/compressor and beautifier toolkit for ES6+ is now available:

https://github.com/adascal/grunt-terser

Great job, it just works as expected.

The harmony branch of grunt-contrib-uglify is deprecated, it's not a sustainable solution.

score 2 · Answer 4 · answered Jan 31 '17 at 10:11

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If the resulting code does not need to use ES6 syntax, it is also possible to transpile ES6 to ES5, before uglifying your code. This can for example be done with the Grunt task grunt-es6-transpiler.

answered Jan 31 '17 at 10:11

gillesB

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score 1 · Answer 5 · answered Aug 07 '17 at 14:48

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I just updated to uglify-js@2.8.29 and it worked.

answered Aug 07 '17 at 14:48

Yoraco Gonzales

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some es6 features are not understood by grunt uglify js?

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