diff --git a/vlib/builtin/js/array.js.v b/vlib/builtin/js/array.js.v
index 8c34829ddd..20f21ff4bd 100644
--- a/vlib/builtin/js/array.js.v
+++ b/vlib/builtin/js/array.js.v
@@ -104,6 +104,13 @@ pub fn (mut a array) insert(i int, val voidptr) {
 	#a.arr.splice(i,0,val)
 }
 
+pub fn (mut a array) join(separator string) string {
+	mut res := ''
+	#res = new builtin.string(a.arr.join(separator +''));
+
+	return res
+}
+
 fn (a array) push(val voidptr) {
 	#a.arr.push(val)
 }
diff --git a/vlib/os_js/environment.js.v b/vlib/os_js/environment.js.v
new file mode 100644
index 0000000000..0f69f094c5
--- /dev/null
+++ b/vlib/os_js/environment.js.v
@@ -0,0 +1,31 @@
+module os_js
+
+// setenv sets the value of an environment variable with `name` to `value`.
+pub fn setenv(key string, val string, overwrite bool) {
+	#if ($process.env[key] && !(overwrite.valueOf())) return;
+	#$process.env[key] = val + '';
+}
+
+// `getenv` returns the value of the environment variable named by the key.
+pub fn getenv(key string) string {
+	mut res := ''
+	#if ($process.env[key]) res = new builtin.string($process.env[key])
+
+	return res
+}
+
+// unsetenv clears an environment variable with `name`.
+pub fn unsetenv(name string) int {
+	#$process.env[name] = ""
+
+	return 1
+}
+
+pub fn environ() map[string]string {
+	mut res := map[string]string{}
+	#for (const key in $process.env) {
+	#res.map.set(key,$process.env[key])
+	#}
+
+	return res
+}
diff --git a/vlib/os_js/file.js.v b/vlib/os_js/file.js.v
new file mode 100644
index 0000000000..a7541c52d3
--- /dev/null
+++ b/vlib/os_js/file.js.v
@@ -0,0 +1,130 @@
+module os_js
+
+pub struct File {
+pub:
+	fd int
+pub mut:
+	is_opened bool
+}
+
+#const $buffer = require('buffer');
+
+// todo(playX):   __as_cast is broken here
+/*
+pub struct ErrFileNotOpened {
+	msg  string = 'os: file not opened'
+	code int
+}
+pub struct ErrSizeOfTypeIs0 {
+	msg  string = 'os: size of type is 0'
+	code int
+}
+fn error_file_not_opened() IError {
+	return IError(&ErrFileNotOpened{})
+}
+fn error_size_of_type_0() IError {
+	return IError(&ErrSizeOfTypeIs0{})
+}
+*/
+pub fn open_file(path string, mode string, options ...int) ?File {
+	mut res := File{}
+	$if js_node {
+		#if (!options) { options = new array([]); }
+		#let permissions = 0o666
+		#if (options.arr.length > 0) { permissions = options.arr[0]; }
+		#try {
+		#res.fd = new int($fs.openSync(''+path,''+mode,permissions))
+		#} catch (e) {
+		#return builtin.error('' + e);
+		#}
+
+		res.is_opened = true
+	} $else {
+		error('cannot open file on non NodeJS runtime')
+	}
+	return res
+}
+
+// open tries to open a file for reading and returns back a read-only `File` object.
+pub fn open(path string) ?File {
+	f := open_file(path, 'r') ?
+	return f
+}
+
+pub fn create(path string) ?File {
+	f := open_file(path, 'w') ?
+	return f
+}
+
+pub fn stdin() File {
+	return File{
+		fd: 0
+		is_opened: true
+	}
+}
+
+pub fn stdout() File {
+	return File{
+		fd: 1
+		is_opened: true
+	}
+}
+
+pub fn stderr() File {
+	return File{
+		fd: 2
+		is_opened: true
+	}
+}
+
+pub fn (f &File) read(mut buf []byte) ?int {
+	if buf.len == 0 {
+		return 0
+	}
+	mut nbytes := 0
+	#try {
+	#let buffer = $fs.readFileSync(f.fd.valueOf());
+	#
+	#for (const val of buffer.values()) { buf.arr[nbytes++] = val; }
+	#}
+	#catch (e) { return builtin.error('' + e); }
+
+	return nbytes
+}
+
+pub fn (mut f File) write(buf []byte) ?int {
+	if !f.is_opened {
+		return error('file is not opened')
+	}
+	mut nbytes := 0
+	#const b = $buffer.Buffer.from(buf.arr.map((x) => x.valueOf()))
+	#try { $fs.writeSync(f.fd.valueOf(),b,0,buf.len.valueOf(),0); } catch (e) { return builtin.error('' + e); }
+
+	return nbytes
+}
+
+// writeln writes the string `s` into the file, and appends a \n character.
+// It returns how many bytes were written, including the \n character.
+pub fn (mut f File) writeln(s string) ?int {
+	mut nbytes := f.write(s.bytes()) ?
+	nbytes += f.write('\n'.bytes()) ?
+	return nbytes
+}
+
+pub fn (mut f File) write_to(pos u64, buf []byte) ?int {
+	if !f.is_opened {
+		return error('file is not opened')
+	}
+	mut nbytes := 0
+	#const b = $buffer.Buffer.from(buf.arr.map((x) => x.valueOf()))
+	#try { $fs.writeSync(f.fd.valueOf(),b,0,buf.len.valueOf(),pos.valueOf()); } catch (e) { return builtin.error('' + e); }
+
+	return nbytes
+}
+
+// write_string writes the string `s` into the file
+// It returns how many bytes were actually written.
+pub fn (mut f File) write_string(s string) ?int {
+	nbytes := f.write(s.bytes()) ?
+	return nbytes
+}
diff --git a/vlib/os_js/os.js.v b/vlib/os_js/os.js.v
new file mode 100644
index 0000000000..2fb088a865
--- /dev/null
+++ b/vlib/os_js/os.js.v
@@ -0,0 +1,95 @@
+module os_js
+
+#const $fs = require('fs');
+#const $path = require('path');
+
+pub const (
+	args = []string{}
+)
+
+$if js_node {
+	#$process.argv.forEach(function(val,index) { args.arr[index] = new string(val); })
+}
+
+// real_path returns the full absolute path for fpath, with all relative ../../, symlinks and so on resolved.
+// See http://pubs.opengroup.org/onlinepubs/9699919799/functions/realpath.html
+// Also https://insanecoding.blogspot.com/2007/11/pathmax-simply-isnt.html
+// and https://insanecoding.blogspot.com/2007/11/implementing-realpath-in-c.html
+// NB: this particular rabbit hole is *deep* ...
+pub fn real_path(fpath string) string {
+	$if js_node {
+		mut res := ''
+		#res = new string( $fs.realpathSync(fpath))
+
+		return res
+	} $else {
+		return fpath
+	}
+}
+
+// flush will flush the stdout buffer.
+pub fn flush() {
+	$if js_node {
+		#$process.stdout.write('')
+	}
+}
+
+// chmod change file access attributes of `path` to `mode`.
+// Octals like `0o600` can be used.
+pub fn chmod(path string, mode int) {
+	$if js_node {
+		#$fs.chmodSync(''+path,mode.valueOf())
+	}
+}
+
+// chown changes the owner and group attributes of `path` to `owner` and `group`.
+// Octals like `0o600` can be used.
+pub fn chown(path string, owner int, group int) {
+	$if js_node {
+		#$fs.chownSync(''+path,owner.valueOf(),group.valueOf())
+	}
+}
+
+pub fn temp_dir() string {
+	mut res := ''
+	$if js_node {
+		#res = new builtin.string($os.tmpdir())
+	}
+	return res
+}
+
+pub fn home_dir() string {
+	mut res := ''
+	$if js_node {
+		#res = new builtin.string($os.homedir())
+	}
+	return res
+}
+
+// join_path returns a path as string from input string parameter(s).
+pub fn join_path(base string, dirs ...string) string {
+	mut result := []string{}
+	result << base.trim_right('\\/')
+	for d in dirs {
+		result << d
+	}
+	mut path_sep := ''
+	#path_sep = $path.sep;
+
+	res := result.join(path_sep)
+	return res
+}
+
+pub fn execute(cmd string) Result {
+	mut exit_code := 0
+	mut stdout := ''
+	#let commands = cmd.str.split(' ');
+	#let output = $child_process.spawnSync(commands[0],commands.slice(1,commands.length));
+	#exit_code = new builtin.int(output.status)
+	#stdout = new builtin.string(output.stdout + '')
+
+	return Result{
+		exit_code: exit_code
+		output: stdout
+	}
+}
diff --git a/vlib/os_js/os.v b/vlib/os_js/os.v
new file mode 100644
index 0000000000..8b4e160ea4
--- /dev/null
+++ b/vlib/os_js/os.v
@@ -0,0 +1,13 @@
+module os_js
+
+pub const (
+	// todo(playX): NodeJS does not seem to have any path limit?
+	max_path_len = 4096
+)
+
+pub struct Result {
+pub:
+	exit_code int
+	output    string
+	// stderr string // TODO
+}
diff --git a/vlib/os_js/process.js.v b/vlib/os_js/process.js.v
new file mode 100644
index 0000000000..392c4a797a
--- /dev/null
+++ b/vlib/os_js/process.js.v
@@ -0,0 +1,173 @@
+module os_js
+
+#const $child_process = require('child_process')
+
+// ProcessState.not_started - the process has not yet started
+// ProcessState.running - the process is currently running
+// ProcessState.stopped - the process was running, but was stopped temporarily
+// ProcessState.exited - the process has finished/exited
+// ProcessState.aborted - the process was terminated by a signal
+// ProcessState.closed - the process resources like opened file descriptors were freed/discarded, final state.
+pub enum ProcessState {
+	not_started
+	running
+	stopped
+	exited
+	aborted
+	closed
+}
+
+// todo(playX): fix reference member access in JS backend
+// [heap]
+pub struct Process {
+pub:
+	filename string
+pub mut:
+	pid    voidptr
+	code   int = -1
+	status ProcessState = .not_started
+	// the current status of the process
+	err           string   // if the process fails, contains the reason why
+	args          []string // the arguments that the command takes
+	env_is_custom bool     // true, when the environment was customized with .set_environment
+	env           []string // the environment with which the process was started  (list of 'var=val')
+	use_stdio_ctl bool     // when true, then you can use p.stdin_write(), p.stdout_slurp() and p.stderr_slurp()
+	use_pgroup    bool     // when true, the process will create a new process group, enabling .signal_pgkill()
+	stdio_fd      [3]int   // the stdio file descriptors for the child process, used only by the nix implementation
+}
+
+// new_process - create a new process descriptor
+// NB: new does NOT start the new process.
+// That is done because you may want to customize it first,
+// by calling different set_ methods on it.
+// In order to start it, call p.run() or p.wait()
+pub fn new_process(filename string) Process {
+	return Process{
+		filename: filename
+		stdio_fd: [-1, -1, -1]!
+	}
+}
+
+// set_args - set the arguments for the new process
+pub fn (mut p Process) set_args(pargs []string) {
+	if p.status != .not_started {
+		return
+	}
+	p.args = pargs
+	return
+}
+
+// set_environment - set a custom environment variable mapping for the new process
+pub fn (mut p Process) set_environment(envs map[string]string) {
+	if p.status != .not_started {
+		return
+	}
+	p.env_is_custom = true
+	p.env = []string{}
+	for k, v in envs {
+		p.env << '$k=$v'
+	}
+	return
+}
+
+fn (mut p Process) spawn_internal() {
+	#p.pid = $child_process.spawn(
+	#p.filename+'',
+	#p.args.arr.map((x) => x.valueOf() + ''),
+	#{
+	#env: (p.env_is_custom ? p.env : $process.env),
+	#})
+	#p.pid.on('error', function (err) { builtin.panic('Failed to start subprocess') })
+
+	p.status = .running
+	// todo(playX): stderr,stdin
+	if p.use_stdio_ctl {
+		#p.pid.stdout.pipe(process.stdout)
+		#p.pid.stdin.pipe(process.stdin)
+		#p.pid.stderr.pipe(process.stderr)
+	}
+}
+
+pub fn (mut p Process) run() {
+	if p.status != .not_started {
+		return
+	}
+	p.spawn_internal()
+	return
+}
+
+pub fn (mut p Process) signal_kill() {
+	if p.status !in [.running, .stopped] {
+		return
+	}
+	#p.pid.kill('SIGKILL');
+
+	p.status = .aborted
+}
+
+pub fn (mut p Process) signal_stop() {
+	if p.status !in [.running, .stopped] {
+		return
+	}
+	#p.pid.kill('SIGSTOP');
+
+	p.status = .aborted
+}
+
+pub fn (mut p Process) signal_continue() {
+	if p.status != .stopped {
+		return
+	}
+	#p.pid.kill('SIGCONT');
+
+	p.status = .running
+	return
+}
+
+pub fn (mut p Process) wait() {
+	if p.status == .not_started {
+		p.spawn_internal()
+	}
+	if p.status !in [.running, .stopped] {
+		return
+	}
+
+	p.wait_internal()
+	return
+}
+
+fn (mut p Process) wait_internal() {
+	#p.pid.on('exit', function (code) { console.log(code) })
+}
+
+pub fn (mut p Process) set_redirect_stdio() {
+	p.use_stdio_ctl = true
+	return
+}
+
+pub fn (mut p Process) stdin_write(s string) {
+	p.check_redirection_call('stdin_write')
+	#p.pid.stdin.write(s)
+}
+
+// todo(playX): probably does not work
+
+// will read from stdout pipe, will only return when EOF (end of file) or data
+// means this will block unless there is data
+pub fn (mut p Process) stdout_slurp() string {
+	p.check_redirection_call('stdout_slurp')
+	mut res := ''
+	#p.pid.stdout.on('data', function (data) { res = new builtin.string(data) })
+
+	return res
+}
+
+// _check_redirection_call - should be called just by stdxxx methods
+fn (mut p Process) check_redirection_call(fn_name string) {
+	if !p.use_stdio_ctl {
+		panic('Call p.set_redirect_stdio() before calling p.$fn_name')
+	}
+	if p.status == .not_started {
+		panic('Call p.${fn_name}() after you have called p.run()')
+	}
+}
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 4811c4a030..0640e64367 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -26,7 +26,7 @@ const (
 	valid_comp_if_platforms     = ['amd64', 'i386', 'aarch64', 'arm64', 'arm32', 'rv64', 'rv32']
 	valid_comp_if_cpu_features  = ['x64', 'x32', 'little_endian', 'big_endian']
 	valid_comp_if_other         = ['js', 'debug', 'prod', 'test', 'glibc', 'prealloc',
-		'no_bounds_checking', 'freestanding', 'threads', 'js_browser', 'js_freestanding']
+		'no_bounds_checking', 'freestanding', 'threads', 'js_node', 'js_browser', 'js_freestanding']
 	valid_comp_not_user_defined = all_valid_comptime_idents()
 	array_builtin_methods       = ['filter', 'clone', 'repeat', 'reverse', 'map', 'slice', 'sort',
 		'contains', 'index', 'wait', 'any', 'all', 'first', 'last', 'pop']
diff --git a/vlib/v/gen/js/js.v b/vlib/v/gen/js/js.v
index a81313f52e..2e8d230e7f 100644
--- a/vlib/v/gen/js/js.v
+++ b/vlib/v/gen/js/js.v
@@ -126,9 +126,10 @@ pub fn gen(files []&ast.File, table &ast.Table, pref &pref.Preferences) string {
 		// builtin types
 		if g.file.mod.name == 'builtin' && !g.generated_builtin {
 			g.gen_builtin_type_defs()
-			g.writeln('Object.defineProperty(array.prototype,"len", { get: function() {return this.arr.length;}, set: function(l) { this.arr.length = l; } }); ')
-			g.writeln('Object.defineProperty(map.prototype,"len", { get: function() {return this.map.length;}, set: function(l) { this.map.length = l; } }); ')
-			g.writeln('Object.defineProperty(array.prototype,"length", { get: function() {return this.arr.length;}, set: function(l) { this.arr.length = l; } }); ')
+			g.writeln('Object.defineProperty(array.prototype,"len", { get: function() {return new builtin.int(this.arr.length);}, set: function(l) { this.arr.length = l.valueOf(); } }); ')
+			g.writeln('Object.defineProperty(string.prototype,"len", { get: function() {return new builtin.int(this.str.length);}, set: function(l) {/* ignore */ } }); ')
+			g.writeln('Object.defineProperty(map.prototype,"len", { get: function() {return new builtin.int(this.map.length);}, set: function(l) { this.map.length = l.valueOf(); } }); ')
+			g.writeln('Object.defineProperty(array.prototype,"length", { get: function() {return new builtin.int(this.arr.length);}, set: function(l) { this.arr.length = l.valueOf(); } }); ')
 			g.generated_builtin = true
 		}