GulpUglifyError:Unable to minify JavaScript

Question

I am trying to minify my script files for which i am using gulp task runner And I am trying gulp-uglify plugin

Code:

 gulp.task(\'concat\', function() {         


        

Answer 1

To see the error in console:

var gutil = require('gulp-util');

gulp.task('concat', function() {
return gulp.src('app/**/*.js')
    // .pipe(concat('script.js'))
    .pipe(uglify())
    .on('error', function (err) { gutil.log(gutil.colors.red('[Error]'), err.toString()); })
    .pipe(gulp.dest('./dist/'))
});

To find the exact file, with line number of error register and run this task:

var pump = require('pump');

gulp.task('uglify-error-debugging', function (cb) {
  pump([
    gulp.src('app/**/*.js'),
    uglify(),
    gulp.dest('./dist/')
  ], cb);
});

Answer 2

Have you used ES6 format in your script file? If so try ES5 now because when you do gulp-uglify it doesnt understand ES6 format as of now and after that try your code

 gulp.task('concat', function() {
    return gulp.src('app/**/*.js')
        .pipe(concat('script.js'))
        .pipe(uglify())
        .pipe(gulp.dest('./dist/'))
});

and run the task gulp concat it will work

Answer 3

you may have syntax error or used ES6 syntax. you can try https://skalman.github.io/UglifyJS-online/ firstly.

Answer 4

For me, it was a deprecated option "preserveComments" that generated the error (and completely crashed the script).

Found the issue using:

gulp.task('concat', function() {
return gulp.src('app/**/*.js')
    .pipe(uglify())
    .on('error', function (err) { console.log( err ) })
    .pipe(gulp.dest('./dist/'))
});

Answer 5

The main error to Unable to minifies JavaScript is the path not found. You can use the task usemin For this you need:

$ sudo npm install gulp-usemin --save-dev
$ sudo npm install gulp-livereload --save-dev
$ sudo npm install gulp-util --save-dev

and requires :

var usemin = require('gulp-usemin');
var livereload = require('gulp-livereload');
var gutil = require('gulp-util'); //gutil for error display

gulp.task('usemin',['jshint'], function(){
    return gulp.src('./app/index.html')
    .pipe(usemin({
        css: [minifycss(),rev()],
        scripts: [uglify().on('error', function(err) {gutil.log(gutil.colors.red('[Error]'), err.toString());this.emit('end');}),rev()]
    })) 
    .pipe(gulp.dest('dist'))
    .pipe(livereload());
});

Change the js: [uglify(), rev()] to scripts: [uglify(), rev()]

Answer 6

The main error is generated when you're using ES6 format. Use the gulp-uglify-es module instead of 'gulp-uglify' to overcome this error.

var uglify = require('gulp-uglify-es').default;

Note: gulp-uglify-es is no longer being maintained. You may want to use terser/gulp-terser instead: