Add possibility to add Attributes

It would be nice if you could easely add attributes. As in, add async or defer attribute to script tags for example.

<script src="demo_async.js" async></script>

[marnusw]

I just found myself wanting to add the async attribute and came across this issue. While overwriting the transform function is certainly easy enough, having async and defer as boolean options passed to inject() would certainly be a nice feature. I think grasping the intent from the code is much easier looking at

inject(sources, {async: true, defer: true})

than

var transform = function (filepath, file, i, length) {
    return '<script src="' + filepath + '" async></script>';
}
inject(source,{transform: transform});

That said, I haven’t looked at the source code, so I have no idea if it’s structured such that this would be an “easy” change. I might look into it at some point and open a PR if there aren’t objections to the idea here in the mean time.

[ceiger89]

Or change default template for html -> js

gulp.task('html', () => {
  inject.transform.html.js = filepath => `<script src="${filepath}" async></script>`;

    return gulp.src('./src/index.html')
        .pipe(inject(gulp.src(['./dev/js/*.js', './dev/css/*.css'], {read: false}), {
            removeTags: true,
            ignorePath: 'dev',
            addRootSlash: false
        }))
        .pipe(gulp.dest('dev'))
});