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Nashorn implements ECMAScript 5.1 specification  http://www.ecma-international.org/ecma-262/5.1/

HTML non-normative version of the spec is here: http://es5.github.io/

Nashorn implements number of syntactic and API extensions as well. This page describes syntax and API extensions of nashorn implementation.

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ECMAScript specifies Object.getPrototypeOf(obj) http://es5.github.io/#x15.2.3.2 function to get prototype of the given object. This Object.setPrototypeOf is a nashorn specific extension that allows prototype of an object to be set by as newProto. Object.setPrototypeOf is one of proposed extensions in ECMAScript 6.

See also https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/setPrototypeOf

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Current executing script file, line, directory of the script can be accessed by these global (read-only) properties. This is useful in debug/tracing scripts. __DIR__ can be used like Unix 'dirname' command. Script can load script-file relative path resources using __DIR__.

print(__FILE__, __LINE__, __DIR__)

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