Uglify SyntaxError: Unexpected token: punc ())

Question

I am trying to use gulp in order to minify a folder containing JS files. However, one of the files has the above error, preventing it from being minified.

I managed to catch and print the error, which I've partially printed here:

JS_Parse_Error {
 message: 'SyntaxError: Unexpected token: punc ())',
 filename: 'ex.js',
 line: 189,
 col: 25,
 pos: 6482,
 stack: Error\n    at new JS_Parse_Error (eval at <anonymous> ... ) 
 plugin: 'gulp-uglify',
 fileName: '.../js/ex.js',
 showStack: false
}

The file in question contains the following, shortened:

function() {
  ...
  $.confirm({
    buttons: {
        confirm: function() {
            $.post('/ajax-handler', {
                    ...
                })
                .done( function(response) {
                    var data = filterResponse(response);
                    if (data['status'] == 'success') {
                        sleep(1000).then(() => {
                    *       ...
                        });
                        sleep(5000).then(() => {
                            ...  
                        });

                    } else {
                        console.log('Oops!');
                    }
                })
                .fail( function(err, status, response) {
                    ...
            });
        },
        cancel: function() {}
    }
 });
  ...
}

I added the "*" above in order to indicate the exact position listed by JS_Parse_Error.

Answer 1

// Update

From the comments ~ @imolit

 v2.0.0 (2018-09-14) - BREAKING CHANGES (link)

Switch back to uglify-js (uglify-es is abandoned, if you need uglify ES6 code please use terser-webpack-plugin).

---

Original answer before the update...

I hope you can get inspired by this solution which works with webpack. (link below)

Simply teach UglifyJS ES6

There are two versions of UglifyJS - ES5 and ES6 (Harmony), see on git
ES5 version comes by default with all the plugins, but if you install a Harmony version explicitly, those plugins will use it instead.

package.json

"uglify-js": "git+https://github.com/mishoo/UglifyJS2.git#harmony"

or

npm install --save uglify-js@github:mishoo/UglifyJS2#harmony

yarn add git://github.com/mishoo/UglifyJS2#harmony --dev

---

Webpack

To use it with webpack install also the webpack plugin

npm install uglifyjs-webpack-plugin --save-dev

yarn add uglifyjs-webpack-plugin --dev

then import the manually installed plugin

var UglifyJSPlugin = require('uglifyjs-webpack-plugin');

and replace it in code

-  new webpack.optimize.UglifyJsPlugin({ ... })
+  new UglifyJSPlugin({ ... })

---

For more webpack info (Installation/Usage) see https://github.com/webpack-contrib/uglifyjs-webpack-plugin#install