nashorn - How to avoid "ReferenceError: "a" is not defined" -


the below code throws referenceerror: "a" not defined. possible avoid , treat variable null?

        scriptengine engine = new scriptenginemanager().getenginebyname("nashorn");         map<string, string> s = new hashmap<string, string>(); //        s.put("a", "a");         bindings bindings = engine.createbindings();         bindings.putall(s);         object res = engine.eval("!a", bindings);         system.out.println(res);

if don't have variable name "a" defined in scope chain, referenceerror should thrown per ecmascript specification. if uncomment line: 

//        s.put("a", "a");

line "a" defined , therefore no referenceerror.

you can check if variable defined or not using "typeof" operator. "typeof == 'undefined'" evaluate false undefined variable "a". won't referenceerror undefined variables. again standard compliant behavior.


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