An issue with undefined and postfix operators

[marccarigiet]

Duktape Version

• Release 2.7.0
• 47eedc5d53

OS

• Ubuntu 20.04

Description
A series of snippets involving undefined and postfix operators that should not be valid JavaScript code don't result in an error on Duktape. The same testcases do result in errors in other JavaScript engines, including V8, Spidermonkey and Jerryscript.

Test cases

undefined ++ . var1 ;

undefined -- . var1 ;

undefined ++ [ this ] ;

Observed behavior
All three snippets evaluate to undefined in Duktape.

Expected behavior
I would expect all three snippets to result in SyntaxErrors.