It appears that in Rhino, doing "myvar = undefined" is the same as doing
EngineBindings.remove(myvar), however in Nashorn the
EngineBindings.remove() operation behaves quite differently.
I've attached a Jython program that I've run under jdk7 and jdk8 that
point up the differences (in /RED italics/):
JAVA 7 (RHINO) JAVA 8 (NASHORN)
Case 1: No longer able to store a value after Bindings.remove().
+----Expr "myvar = 33" +----Expr "myvar = 33"
myvar = 33 myvar = 33
Bindings.remove(myvar) Bindings.remove(myvar)
Engine.eval('myvar'): FAILED Engine.eval('myvar'): FAILED
typeof(myvar)=undefined typeof(myvar)=undefined
myvar in bindings: False myvar in bindings: False
myvar = 33 myvar = 33
/Engine.eval('myvar'): 33 Engine.eval('myvar'): FAILED//
// typeof(myvar)=number typeof(myvar)=undefined//
// myvar in bindings: True myvar in bindings: False/
Case 2: Bindings.remove() does not remove the value.
+----Expr "var myvar=33" +----Expr "var myvar=33"
var myvar=33 var myvar=33
Bindings.remove(myvar) Bindings.remove(myvar)
/Engine.eval('myvar'): FAILED Engine.eval('myvar'): 33//
// typeof(myvar)=undefined typeof(myvar)=number//
// myvar in bindings: False myvar in bindings: True/
var myvar=33 var myvar=33
Engine.eval('myvar'): 33 Engine.eval('myvar'): 33
typeof(myvar)=number typeof(myvar)=number
myvar in bindings: True myvar in bindings: True
We previously used Bindings.remove('myvar') and could not understand
Nashorn's behavior. We've switched to using "myvar = undefined" and
everything seems fine now.
Nonetheless, can someone explain why doing Bindings.remove("var") shows
this behavior?
Thank you,
Eric Woudenberg
# Investigate the funny behavior of remove
from javax.script import ScriptEngineManager, ScriptContext
#from java.lang import System
#System.setProperty('nashorn.args','--global-per-engine')
def show(ref):
try:
print " Engine.eval('%s'):" % ref, Engine.eval('%s' % ref)
except:
print "FAILED"
print ' typeof(%s)=%s' % (ref, Engine.eval('typeof(%s)' % ref))
print ' myvar in bindings:', 'myvar' in Bindings
def run_setundefined(expr, ref):
print '\n %s' % expr
Engine.eval(expr, Bindings)
Engine.eval('%s=undefined' % ref)
print " %s=undefined" % ref
show(ref)
Engine.eval(expr, Bindings)
print ' %s' % expr
show(ref)
def run_removebinding(expr, ref):
print '\n %s' % expr
Engine.eval(expr, Bindings)
#show(ref)
Bindings.remove(ref)
print " Bindings.remove(%s)" % ref
show(ref)
Engine.eval(expr, Bindings)
print ' %s' % expr
show(ref)
def main():
global Engine, Bindings
Engine = ScriptEngineManager().getEngineByName("JavaScript")
ref = 'myvar'
sequence = 'myvar = 33', 'var myvar=33', 'this.myvar = 33'
print '********** using Bindings.remove(myvar) **********'
for expr in sequence:
Bindings = Engine.createBindings()
Engine.setBindings(Bindings, ScriptContext.ENGINE_SCOPE)
print '\n+----Expr "%s"' % expr
run_removebinding(expr, ref)
print '\n********** using "myvar = undefined" **********'
for expr in sequence:
Bindings = Engine.createBindings()
Engine.setBindings(Bindings, ScriptContext.ENGINE_SCOPE)
print '\n+----Expr "%s" Ref %s ' % (expr, ref)
run_setundefined(expr, ref)
main()
