JSFileApi

File is an immutable object. To mutate it, just create new File()s.

var dir = new File("/path"); // /path on unix
var subdir = new File(dir, "name.txt") // /path/name.txt on unix

File.path is the relative path
File.absolutePath()
File.resolveLinks()
File.stat() returns a new immutable objects describing the file eg {isDirectory:true, isFile:false, lastModified, ...} 

File.readdir() returns an array of arrays(because we don't have tuples)
//readdir throws an exception if it isn't a directory
for each [file,stat_info] in file.readdir() {
 // stat_info is akin to the info returned by stat(), but it only has the information returned by readdir(3) in it(ie is this a file/dir/etc), rest of the properties are lazily computed by doing a lazy stat() call. 
 // here type is a directory|file.
 i = file.stat()
 // i = { size: 1, lastModified:...}
}

IO

File.open should be similar to the unix open.

var desc = File.open([File.WRITE_ONLY, File.CREATE])
desc.write("foo");
desc.close()
var d2 = File.open([File.READ])
d2.seek(...)
var contents = d2.read()// with optional size parameter to read less than full remaining file 
d2.close()