Call javascript that contains 'const' from java?

Question

I am trying to use a transpiling tool that has been developed in js and was available in GitHub. This transpiler is capable to convert the javascript code to java.

I want to call the tool via java code so that I could read js files in java and process them using the transpiler developed in JS. The tool is using 'const' as part of its code. While using ScriptEngine it gives me an exception. Please help!!

Sample Code:

public static void main(String[] args) {

    ScriptEngineManager manager = null;
    ScriptEngine engine = null;
    File folder = null;

    try {

        manager = new ScriptEngineManager();
        engine = manager.getEngineByName("nashorn");
        String testConst1 = (String) "const pi = 3.14;";
        String testPrint1 = (String) "function hello(name) {print ('Hello, ' + name +' = '+ pi);}";
        engine.eval(testConst1);
        engine.eval(testPrint1);

        Invocable inv = (Invocable) engine;
        inv.invokeFunction("hello", "pi");
        // System.out.println(); //This one works.

    } catch (Exception e) {
        e.printStackTrace();
    }
}

This piece of code gives me below stack trace.

javax.script.ScriptException: <eval>:1:0 Expected an operand but found const
const pi = 3.14;
^ in <eval> at line number 1 at column number 0
at jdk.nashorn.api.scripting.NashornScriptEngine.throwAsScriptException(NashornScriptEngine.java:455)
at jdk.nashorn.api.scripting.NashornScriptEngine.compileImpl(NashornScriptEngine.java:522)
at jdk.nashorn.api.scripting.NashornScriptEngine.compileImpl(NashornScriptEngine.java:509)
at jdk.nashorn.api.scripting.NashornScriptEngine.evalImpl(NashornScriptEngine.java:397)
at jdk.nashorn.api.scripting.NashornScriptEngine.eval(NashornScriptEngine.java:152)
at javax.script.AbstractScriptEngine.eval(Unknown Source)

Caused by: jdk.nashorn.internal.runtime.ParserException: <eval>:1:0 Expected an operand but found const
const pi = 3.14;
^
at jdk.nashorn.internal.parser.AbstractParser.error(AbstractParser.java:292)
at jdk.nashorn.internal.parser.AbstractParser.error(AbstractParser.java:277)
at jdk.nashorn.internal.parser.Parser.unaryExpression(Parser.java:3175)
at jdk.nashorn.internal.parser.Parser.expression(Parser.java:3275)
at jdk.nashorn.internal.parser.Parser.expressionStatement(Parser.java:1152)
at jdk.nashorn.internal.parser.Parser.statement(Parser.java:969)
at jdk.nashorn.internal.parser.Parser.sourceElements(Parser.java:775)
at jdk.nashorn.internal.parser.Parser.program(Parser.java:711)
at jdk.nashorn.internal.parser.Parser.parse(Parser.java:284)
at jdk.nashorn.internal.parser.Parser.parse(Parser.java:250)
at jdk.nashorn.internal.runtime.Context.compile(Context.java:1207)
at jdk.nashorn.internal.runtime.Context.compileScript(Context.java:1179)
at jdk.nashorn.internal.runtime.Context.compileScript(Context.java:594)
at jdk.nashorn.api.scripting.NashornScriptEngine.compileImpl(NashornScriptEngine.java:520)
... 5 more

score 8 · Answer 1 · answered Jun 11 '17 at 03:56

With --language=es6 option, nashorn supports "const" keyword.

$ jjs --language=es6 
jjs> const x = 44

If you're programmatically creating Nashorn script engine, you can still pass options to Nashorn using "nashorn.args" System property.

File Main.java:

import javax.script.*;

public class Main {
    public static void main(String[] args) throws Exception {
        ScriptEngineManager m = new ScriptEngineManager();
        ScriptEngine e = m.getEngineByName("nashorn");
        e.eval("const X = 44; print(X)");
    }
}


$ javac Main.java

$ java Main

Exception in thread "main" javax.script.ScriptException: <eval>:1:0 Expected an operand but found const
const X = 44; print(X)
^ in <eval> at line number 1 at column number 0
    at jdk.nashorn.api.scripting.NashornScriptEngine.throwAsScriptException(NashornScriptEngine.java:470)
    at jdk.nashorn.api.scripting.NashornScriptEngine.compileImpl(NashornScriptEngine.java:537)
    at jdk.nashorn.api.scripting.NashornScriptEngine.compileImpl(NashornScriptEngine.java:524)
    at jdk.nashorn.api.scripting.NashornScriptEngine.evalImpl(NashornScriptEngine.java:402)
    at jdk.nashorn.api.scripting.NashornScriptEngine.eval(NashornScriptEngine.java:155)
    at javax.script.AbstractScriptEngine.eval(AbstractScriptEngine.java:264)
    at Main.main(Main.java:7)

$ java -Dnashorn.args=--language=es6 Main
44

See here -> https://wiki.openjdk.java.net/display/Nashorn/Nashorn+jsr223+engine+notes

Thanks, it is also possible to pass the option to Nashorn directly: `ScriptEngine engine = new NashornScriptEngineFactory().getScriptEngine("--language=es6");` — Eugene, May 20 '23 at 05:35

score 1 · Answer 2 · answered Jun 10 '17 at 19:23

What is the script engine you used ?

Anyway that is because some javaScript engines does not recognize const keyword. (ex: Nashorn does not recognize it).

In this book it says something like, "This option is available if a script uses the const keyword, which is not recognized by Nashorn."

And it has some existing bugs filed,

Call javascript that contains 'const' from java?

2 Answers2