GulpUglifyError: unable to minify JavaScript Caused by: SyntaxError: Unexpected token name «k», expected punc «;»

Question

I am getting some strange error, but in order to suppress these error I have to change everything where I am getting error?

//gulp file code
var fs = require('fs');
var path = require('path');`enter code here`
var merge = require('merge-stream');
var gulp = require('gulp');
var concat = require('gulp-concat');
var rename = require('gulp-rename');
var uglify = require('gulp-uglify');
var sourcemaps = require('gulp-sourcemaps');
var gutil = require('gulp-util');



gulp.task('css',function()
{

return gulp.src(['assets/css/*.css'])
    .pipe(sourcemaps.init())

    .pipe(sourcemaps.write())
    .pipe(uglify())
    .on('error', function (err) { gutil.log(gutil.colors.red('[Error]'), err.toString()); })
    .pipe(concat('all.css'))
    .pipe(gulp.dest('build/css'))

})
gulp.task('js',function()
{

return gulp.src(['shared/*.js','controller/*.js','directives/*.js','services/*.js'])
    .pipe(sourcemaps.init())

    .pipe(sourcemaps.write())
    .pipe(uglify())
    .on('error', function (err) { gutil.log(gutil.colors.red('[Error]'), err.toString()); })
    .pipe(concat('all.js'))
    .pipe(gulp.dest('build/js'))

})

gulp.task('default', ['css','js']);

I tried to find the solution online, but no luck

for (let k = 0; k < $scope.allCollctedTags.length; k++) 
{
 $scope.customtags.push($scope.allCollctedTags[k].text);
}

but if I replace let with var then this error removed now next error come for the following code:

$scope.multipleImages.push(...response.data.result.imageName);
but if i write it as below then this error disappear
$scope.multipleImages.push(response.data.result.imageName);

also if i use underscore js then also it give me error 
let temparray = _.difference($scope.multipleImages,$scope.extractedImagesBrowse);

Now what to do, I can do these things in one or two files but for the whole project I cannot do it.

Answer 1

Following this answer, what I found was that I tried to compile code that was not parsable with the ugilfy version that I had. Try using ugifly-es instead of pure uglify package:

const uglify = require("gulp-uglify");

To:

const uglify = require("gulp-uglify-es");

And make sure you have the package installed.

Also, if you don't want to use unsupported package, take a look at this answer as it covers your issue: