I want to execute JavaScript function from Java. I used the following piece of code

ScriptEngineManager manager = new ScriptEngineManager();    
ScriptEngine engine = manager.getEngineByName("JavaScript"); 

but this throws an exception for the alert() method ?

engine.eval("alert('HI');");

I want to execute JavaScript function from Java. I used the following piece of code

ScriptEngineManager manager = new ScriptEngineManager();    
ScriptEngine engine = manager.getEngineByName("JavaScript"); 

but this throws an exception for the alert() method ?

engine.eval("alert('HI');");

• javascript
• java

• Try eval("alert(\"HI\")"); – OneCricketeer Commented Dec 20, 2015 at 17:49

4 Answers 4

So. I'm pretty sure your code here is incorrect.

engine.eval("alert(HI);");

Try.

engine.eval("alert('Hi');");

unless you have a variable HI declared.

you can not call javascript from java in any way. javascript is client side language and executed on browser where as java is executed on server

Update :- Thanks guys i learnt something new here.

when i execute the code in op i get below error

Error executing script: ReferenceError: "alert" is not defined in <eval> at line number 1

Reason is alert is not part of JavaScript, it's part of the window object provided by web browsers.so, Nashhorn javascript engine does not know about it.

Please see ReferenceError: "alert" is not defined

It appears that "alert()" is part of the window object provided by web browsers. it doesn't exist here

I have modified java code:

ScriptEngineManager manager = new ScriptEngineManager();      
ScriptEngine engine  = manager.getEngineByName("JavaScript");
engine.eval("print('HI');");

This is useful: Java Scripting Programmer's Guide
Information about javscript window object: The Window Object

You are doing it the wrong way, you cannot call JavaScript function from java code because one is executed at client side and other at server side...even if you achieve that using some API it's wrong way of architecturing of code.