Gulp-Jscover-1.js

var elixir = require('laravel-elixir');
var gulp = require('gulp');
var gulpUtil = require('gulp-util');
var instrument = require('gulp-instrument');

Gulp-Jscover-2.js

elixir(function (mix) {
    if (gulpUtil.env.production) {
        console.log('production build');

        // combine to all.js
        mix.scripts([
           './Scripts/active.js',
           './Scripts/myscript2.js'
        ], 'public/js/'); // output location

    }
    else {
        console.log('dev build');
        mix.task('instrument');
    }
});

gulp.task('instrument', function () {
    console.log('instrument files');

    return gulp.src('Scripts/active.js') // use 'Scripts/**.js' for all scripts
      .pipe(instrument())
      .pipe(gulp.dest('public/js')); // output location 
});