var ts = require('gulp-typescript');
var concat = require('gulp-concat');
var sourcemaps = require('gulp-sourcemaps');
var cleants = require('gulp-clean-ts-extends');

gulp.task('scripts', function() {
    var tsResult = gulp.src('lib/*.ts')
                       .pipe(sourcemaps.init())
                       .pipe(ts({
                           sortOutput: true,
                           // ...
                       }));

    return tsResult.js
                .pipe(concat('output.js'))
                .pipe(cleants()) // remove all __extends declarations except the first one
                .pipe(sourcemaps.write())
                .pipe(gulp.dest('release/js'));
});