allow javascript to control some environmental things - javascript

I want to use GraalVM to run user-written javascript code (I am writing a Java 11 project).
Can I give Java objects to the javascript file, in javascript I want to write something like
shrek.shedLayer();
and when my Java program executes this statement it is equivalent to as if it (the java program) had directly run
someLong.pieceOf().Code();
Maybe multipleLines = new Maybe();
someLong.add(multipleLines);
or whatever.

Yes, you can have your Java code evaluate JavaScript. Yes, you can pass Java objects to the JavaScript context. Yes, you can return JavaScript values into Java.
Here's an example of the Java code that instantiates a JavaScript context, evaluates a string of JavaScript code that defines a function, stores this function in a variable, calls it passing Java objects as parameters and prints the return value of this function invocation.
import org.graalvm.polyglot.*;
import java.io.File;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.stream.Stream;
public class ExtListDir {
public static void main(String[] args) throws java.io.IOException {
final Context context = Context.create("js");
String s = "name + ': ' + size";
if (args.length == 1) {
s = args[0];
}
final Value lambda = context.eval("js",
"(function(name, size) { return " + s + "})");
try (Stream<Path> paths = Files.walk(Paths.get("."))) {
paths.filter(Files::isRegularFile).forEach((Path p) -> {
File f = p.toFile();
Value v = lambda.execute(f.getName(), f.length());
System.out.println(v);
});
}
}
}
If you want to use Java classes from the JS context, you can reference them with Java.type(), for example here's a JS snippet which uses Java's BigInteger:
const BigInteger = Java.type('java.math.BigInteger');
var text = BigInteger.valueOf(10).pow(100)
.add(BigInteger.valueOf(43)).toString();

Related

Kotlin Call Javascript function in Android without webView

Is there any way we can call JS function from Kotlin without having WebView in Android?
Let's say as mentioned below I have one JS function helloJS() in test.js file,
test.js:-
function helloJS(){
return "Hello from JS"
}
And now I want to call this function from Kotlin file like
TestClass.kt:-
class TestHello{
fun getHelloFromJS(){
val name = test.helloJS()
}
}
Till now I am using Webview and loading JS file into that and getting result as call back
But, I read that Kotlin is interoperable with JS like Java
So I am curious to know if there is any way we can use that on Android without having webView
This is not possible straight forward but I found one library Execute JavaScript in Android without WebView for achieve this.
Read that blog carefully and follow below step.
Keep your JavaScript file (test.js) in assets folder in android project.
I have converted that code into Kotlin.
CallJavaScript.jks
import org.mozilla.javascript.Context
import org.mozilla.javascript.Function
import java.io.InputStreamReader
object CallJavaScript {
fun callFunction(mContext: android.content.Context): Any? {
var jsResult: Any? = null
val params = arrayOf<Any>("")
// Every Rhino VM begins with the enter()
// This Context is not Android's Context
val rhino = Context.enter()
// Turn off optimization to make Rhino Android compatible
rhino.optimizationLevel = -1
try {
val scope = rhino.initStandardObjects()
// Note the forth argument is 1, which means the JavaScript source has
// been compressed to only one line using something like YUI
val assetManager = mContext.assets
try {
val input = assetManager.open("test.js")
val targetReader = InputStreamReader(input)
rhino.evaluateReader(scope, targetReader, "JavaScript", 1, null)
} catch (e: Exception) {
e.printStackTrace()
}
// Get the functionName defined in JavaScriptCode
val obj = scope.get("helloJS", scope)
if (obj is Function) {
// Call the function with params
jsResult = obj.call(rhino, scope, scope, params)
// Parse the jsResult object to a String
val result = Context.toString(jsResult)
}
} finally {
Context.exit()
}
return jsResult
}
}
Add this line to build.gradle:
implementation 'org.mozilla:rhino:1.7R4'
In your assets folder, create a file called test.js:
function helloJS()
{
return "Hello from JS";
}
Now simply call above function from Activity.
Log.e("JS : ", CallJavaScript.callFunction(this).toString());
Output :
E/JS :: Hello from JS
It's not possible. You must not confuse the language with the platform.
Kotlin is interoperable with JS like Java
means Kotlin/JS can use and be used in a Javascript platform (Node.js or browsers). The Kotlin code compiled (transpiled) into js is able to call other js files. And external Js code can call the js code build from Kotlin. This is the interoperability with JS.
There is no interoperability between Kotlin/JS and Kotlin/JVM.
Kt looks like JS, but it is not. It will be compiled for Android runtime, not for the java script engine.
JS code require a JS runtime, but it is not in Android Runtime.
i.e. you cannot run JS directly in Java / Kt code for Android.
Am not a pro in Kotlin but Java is a pie for me. Anything you can implement in Java can be implemented in Kotlin and To execute Javascript code, I use rhino which does the job pretty easier than using the webview
Implement it:
try {
Scriptable scope = rhino.initStandardObjects();
rhino.evaluateString(scope, javaScriptCode, "JavaScript", 1, null);
Object obj = scope.get(functionNameInJavaScriptCode, scope);
if (obj instanceof Function) {
Function jsFunction = (Function) obj;
// Call the function with params
Object jsResult = jsFunction.call(rhino, scope, scope, params);
// Parse the jsResult object to a String
String result = Context.toString(jsResult);
}
}finally {
Context.exit();
}

What is the use of overriding hasMember() inside JSObject, AbstractJSObject?

I understand that this helper method can be called from a Java code to check if your Java/JS Object has a property you are looking for
but i would like to know if this is called by the Nashorn Engine while we use this JSObject/AbstractJSObject implementation in a JavaScript code.
I am aware of the fact that doing a . inside JavaScript will in turn invoke the Java method .getMember()
If "in" operator in used in JavaScript (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/in) on a JSObject instance, Nashorn will call hasMember method on that JSObject.
Example code:
import javax.script.*;
import jdk.nashorn.api.scripting.*;
public class Main {
public static void main(String[] args) throws Exception {
ScriptEngineManager m = new ScriptEngineManager();
ScriptEngine e = m.getEngineByName("nashorn");
e.put("obj", new AbstractJSObject() {
#Override
public boolean hasMember(String name) {
System.out.println("hasMember called for " + name);
return false;
}
});
// in operator triggers hasMember call on JSObject instance
e.eval("if ('foo' in obj) print('yes')");
}
}
The output from the above program looks like:
hasMember called for foo

Can I run JavaScript inside Swift code?

I need to include JavaScript code in Swift code to be able to call a signalR chat, is that possible? If not, can I convert it?
sendmessage is a button.
$(function () {
// Declare a proxy to reference the hub.
var chat = $.connection.chatHub;
// Create a function that the hub can call to broadcast messages.
chat.client.broadcastMessage = function (name, message) {
// some code
};
// Start the connection.
$.connection.hub.start().done(function () {
$('#sendmessage').click(function () {
// Call the Send method on the hub.
chat.server.send('name', 'message');
});
});
});
and the signalr code is:
public void Send(string name, string message)
{
// Call the broadcastMessage method to update clients.
Clients.All.broadcastMessage(name, message);
}
Update #1:
changed question a little bit so it is not confusing per #MartinR
Last tested with Swift 5.1
Here is an example you can run in Playground to get you started:
import JavaScriptCore
let jsSource = "var testFunct = function(message) { return \"Test Message: \" + message;}"
var context = JSContext()
context?.evaluateScript(jsSource)
let testFunction = context?.objectForKeyedSubscript("testFunct")
let result = testFunction?.call(withArguments: ["the message"])
result would be Test Message: the message.
You also can run JavaScript code within a WKWebView calling evaluate​Java​Script(_:​completion​Handler:​).
You can also run JavaScript within a UIWebView by calling string​By​Evaluating​Java​Script(from:​), but note that that method has been deprecated and is marked as iOS 2.0–12.0.
Using JavaScriptCore framework include JavaScript code in Swift code.
The class that you’ll be dealing the most with, is JSContext. This class is the actual environment (context) that executes your JavaScript code.
All values in JSContext, are JSValue objects, as the JSValue class represents the datatype of any JavaScript value. That means that if you access a JavaScript variable and a JavaScript function from Swift, both are considered to be JSValue objects.
I strongly advise you to read the official documentation regarding the JavaScriptCore framework. 
import JavaScriptCore
var jsContext = JSContext()
// Specify the path to the jssource.js file.
if let jsSourcePath = Bundle.main.path(forResource: "jssource", ofType: "js") {
do {
// Load its contents to a String variable.
let jsSourceContents = try String(contentsOfFile: jsSourcePath)
// Add the Javascript code that currently exists in the jsSourceContents to the Javascript Runtime through the jsContext object.
self.jsContext.evaluateScript(jsSourceContents)
}
catch {
print(error.localizedDescription)
}
}
more details refer this tutorial

export function to global scope in scalajs

Question about scalajs and javascript.
How to mark a function to be purely exported to global scope?
Given scala object in top level package
#JSExport
object Foo{
def apply(a: Int, b: Int): String = "bar"+a+b
}
I would like to compile this scala code into javascript and have this function named Foo in global scope. In other words I would like to have a javascript similar to this:
function Foo(a,b) {
return 'bar'+a+b;
}
Is it possible using scalajs?
I am writing component in javascript, which will be referenced from third party API which can not be influenced by me. This is why I simply need to follow their rules and provide javascript functions in global scope.
The solution to this is now Top Level Exports, as documented under the now-closed issue #1381 - to use this feature, tag a function in an object with #JSExportTopLevel.
object A {
#JSExportTopLevel("foo")
def foo(x: Int): Int = x + 1
}
<Foo will be available from JavaScript's global namespace>
(See https://www.scala-js.org/doc/interoperability/export-to-javascript.html for the official documentation, under "Exporting top-level methods".)
You currently cannot do this without executing some code. But you can have setup code that assigns it:
import scala.scalajs.js
object App extends js.JSApp {
def main(): Unit = {
js.Dynamic.global.anything = // your js.FunctionN
}
}
There is an issue open (#1381) to have language support for this.

Equivalent of Ruby's "require" in Javascript

How do you "require" another file into the existing file in Javascript? Is there anything similar to Ruby's "require" or "load"?
> Note: I'm using JS in server (Rhino)
Reason: I just need to access the methods in the other JS files.
Update: This works only when executing it from cmd line. When I try to call it programatically it fails. Here's my code: http://pastie.org/1240495
To use the load function in js embedded from Java, you must first expose it in on the scripting context. There's probably a way to do it from Java, but you can do it using js as well.
Disclaimer: this solution uses source code taken from an Apache-licensed project I have been working on. You can see the original source file here.
This js file sets up your global variables, and lives in a file named setupglobals.js:
var shell = org.mozilla.javascript.tools.shell.Main;
var args = ["-e","var a='STRING';"];
shell.exec(args);
var shellGlobal = shell.global;
//grab functions from shell global and place in current global
load=shellGlobal.load;
print=shellGlobal.print;
defineClass=shellGlobal.defineClass;
deserialize=shellGlobal.deserialize;
doctest=shellGlobal.doctest;
gc=shellGlobal.gc;
help=shellGlobal.help;
loadClass=shellGlobal.loadClass;
quit=shellGlobal.quit;
readFile=shellGlobal.readFile;
readUrl=shellGlobal.readUrl;
runCommand=shellGlobal.runCommand;
seal=shellGlobal.seal;
serialize=shellGlobal.serialize;
spawn=shellGlobal.spawn;
sync=shellGlobal.sync;
toint32=shellGlobal.toint32;
version=shellGlobal.version;
environment=shellGlobal.environment;
Here is your original Java host file, now augmented to evaluate setupglobals.js before any other scripts:
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import org.mozilla.javascript.*;
public class RhinoRunner {
public static void main(String args[]) throws IOException
{
BufferedReader script = new BufferedReader(new FileReader("setupglobals.js"));
BufferedReader script2 = new BufferedReader(new FileReader("example.js"));
Context context = Context.enter();
try {
ScriptableObject scope = context.initStandardObjects();
context.evaluateReader(scope, script, "script", 1, null);
context.evaluateReader(scope, script2, "script2", 1, null);
Function fct = (Function)scope.get("abc", scope);
Object result = fct.call(context, scope, scope, new Object[] {2, 3});
System.out.println(Context.jsToJava(result, int.class));
}
finally
{
Context.exit();
}
}
}
Here is your example.js, now augmented to use the global load function to load the file hello.js:
function abc(x,y)
{
return x+y
}
load("hello.js")
And finally, here is hello.js:
print("hello world!")
When executed, RhinoRunner prints the following:
hello world!
5
In Rhino shell, you can should be able to use load(), which is a predefined global method:
load([filename, ...])
Load JavaScript source files named by string arguments. If multiple arguments are given, each file is read in and executed in turn.

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