Recursively search for files in directories

RecursiveFileSearch.js

/*
 Given collection like: 
 ```
	const fileData = {
    	dir : 'app',
        files : [
            'index.html',
            {
                dir : 'js',
                files: [
                    'main.js',
                    'app.js',
                    'misc.js',
                    {
                        dir : 'vendor',
                        files : [
                            'jquery.js',
                            'underscore.js'
                        ]
                    }
                ]
            },
            {
                dir : 'css',
                files : [
                    'reset.css',
                    'main.css'
                ]
            }
        ]
    };
```	
return list of all files or files in given directory

*/
const searchFiles = (data, dirName) => {
  const isString = value => typeof value === 'string';

  const generateListInDir = data => {
    return data.files.reduce((filesList, file) => {
      return isString(file)
        ? [...filesList, file]
      	: [...filesList, ...generateListInDir(file)];
    }, []);
  };

  if (dirName) {
    return dirName === data.dir
      ? generateListInDir(data)
      : data.files
        .filter(fileName => !isString(fileName))
        .reduce((branchFiles, branch) => {
      		return [...branchFiles, ...this.listFiles(branch, dirName)];
      	}, []);
  } else {
    return generateListInDir(data);
  }
}