normalizePath(output, fallback) {
        // All output paths need to start at the project's public dir.
        let pathFromPublicDir = output.pathFromPublic();
        if (
            !pathFromPublicDir.startsWith('/' + this.mix.config.publicPath) &&
            !pathFromPublicDir.startsWith('\\' + this.mix.config.publicPath)
        ) {
            output = new File(
                path.join(this.mix.config.publicPath, output.pathFromPublic())
            );
        }

        // If the output points to a directory, we'll grab a file name from the fallback src.
        if (output.isDirectory()) {
            output = new File(
                path.join(output.filePath, fallback.nameWithoutExtension() + '.js')
            );
        }

        return output;
    }
Normalize the given output path.

@param {File} output
@param {File} fallback