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Strongly-Typed Javascript (STJS)

Build Status

STJS is an open source (Apache 2.0 licensed) Javascript code generator from a Java source. It is built as a Maven plugin that can be executed after the compilation of your Java code.

Our full website can be found at

Compiling the Project

ST-JS compiles with the traditional mvn install command, but it currently needs both Java 6 - that is the default JDK on the command line when you call the Maven command, but also Java 8 to compile the generator-plugin-java8 artifact. To achieve this, you need to to configure the environment variable JAVA8_HOME that points to the home of your JDK 8 home folder.

Notes on Primitives+Arrays Support


AnyNonPrimitiveType[] is Array

String[] a = {"a", "b"};
var a = ["a", "b"];

Multidimensional arrays

float[][][] arr = new float[1][2][3];
Object[][][] objarr = new Object[][][]{ new String[][]{ { "hello" }, { "world" }, new String[]{} }, new Integer[][]{ { 1, 2 }, { 3, 4 } }, new Double[4][5] };
var arr = Array.apply(null, Array(1)).map(function(){return Array.apply(null, Array(2)).map(function(){return new Float32Array(3);});});"
var objarr = [[["hello"], ["world"], []], [[1, 2], [3, 4]], Array.apply(null, Array(4)).map(function() { return Array(5);})];

Primitive Arrays

Java JavaScript
boolean[] Int8Array
byte[] Int8Array
short[] Int16Array
char[] Uint16Array
int[] Int32Array
float[] Float32Array
double[] Float64Array
long[] Array


Enhanced for loop over Java arrays will iterate over values instead of keys

String[] msg = {"hello", "world"};
for(String s : msg) {
var msg = ["hello", "world"];
for(var index$s = 0, arr$s = msg; index$s < arr$s.length; index$s++) {
	var s = arr$s[index$s];


There is no support for 64bit integer type in JavaScript. Max value for an integer is 2^53-1



char is stored in Java as unsigned short so it is in st-js primitive support.

char[] in st-js is Uint16Array.

The following side effects appear:

String a = "hello worl";
char c = 'd';
String result = a + c;
var a = "hello worl";
var c = 'd'.charCodeAt(0); //looks ugly but compatible
var result = a + String.fromCharCode(c);
char c = 'a';
byte b = (byte) c;
var c = 'a'.charCodeAt(0);
var b = c << 24 >> 24;

float and double

Are considered equivalent no attempt for Java compatibility is made.

primitive type casting

Java JavaScript
int to short ((i)<<16>>16)
int to byte ((i)<<24>>24)
int to char ((i)&0xfff)
int to long var l = i
int to float var f = i
int to double var d = i
short to byte ((s)<<24>>24)
short to char ((s)&0xfff)
short to int var i = s
short to long var l = s
short to float var f = s
short to double var d = s
byte to short var s = b
byte to char var c = b
byte to int var i = b
byte to long var l = b
byte to float var f = b
byte to double var d = b
char to byte ((c)<<24>>24)
char to short var s = c
char to int var i = c
char to long var l = c
char to float var f = c
char to double var d = c
long to byte ((l)<<24>>24)
long to short ((l)<<16>>16)
long to char ((l)&0xfff)
long to int var i = l|0
long to float var f = l
long to double var d = l
float to byte ((f)<<24>>24)
float to short ((f)<<16>>16)
float to char ((f)&0xfff)
float to int var i = f|0
float to long var l = stjs.trunc(f)
float to double var d = f
double to byte ((d)<<24>>24)
double to short ((d)<<16>>16)
double to char ((d)&0xfff)
double to int var i = d|0
double to long var l = stjs.trunc(d)
double to float var f = d