function testDeflUndefinedForNumber ( f , g ? ) { assert ( f == 3 , "t3" ) ; assert ( g == null , "n3" ) ; assert ( g === undefined , "n3" ) ; } function checkJSON ( ) { msg ( "JSON" ) ; testDeflUndefinedForNumber ( 3 ) ; let ss = "12" + "34" ; assert ( ss . slice ( 1 ) == "234" , "sl0" ) ; assert ( ss . slice ( 1 , 2 ) == "2" , "sl1" ) ; assert ( ss . slice ( - 2 ) == "34" , "sl2" ) ; assert ( ss . slice ( 1 , 0 ) == "" , "sl3" ) ; assert ( ss . slice ( 1 , - 1 ) == "23" , "sl4" ) ; let v = { foo : 1 , bar : "foo" , baz : [ 1 , 2 ] } ; } checkJSON ( ) ;