An issue about evaluating instanceof

According to ES10.0, If an object does not define or inherit @@hasInstance it uses the default instanceof semantics. When changing the value of __proto__ of an object into String, the algorithm to be used will be Function.prototype [ @@hasInstance ] instead of the default semantics. So the output of the testcase below is false as other engines do. This may be an issue of chakra.

version

v1.11.19

command

 chakra/cc_linux_x64_1_11_19/ChakraCoreFiles/bin/ch testcase.js

testcase

var  obj = {__proto__:String};
var result = "hello" instanceof obj;
print(result);

output

TypeError: obj is not a function. (evaluating '"hello" instanceof obj')

expected output

false

contributor:@YuanWangC

[rhuanjl]

1st. Can you build ChakraCore? If you’re on windows point visual studio at Build\Chakra.Core.sln Check that you can build it, I reccomend the x64 debug configuration for testing.

2nd. Make a javascript file that reproduces the above error, run it from the command line with ch.exe (which will have been built as part of step 1)

3rd. Have a look in the ChakraCore codebase for JavascriptOperators::OP_IsInst (it’s in the file: lib/Runtime/Language/JavascriptOperators.cpp) explore what this function is doing and how/when/why it can fail to check an object’s prototype. (This may not be the source of the error - but it appears to be at first glance), you’ll probably need to repeatedly rebuild and test examples with ch.exe to figure out how to get this working properly.

4th. If you can get it working you’ll need to add a suitable test to our test suite - tag me for help again there if it’s not obvious how to do it.

[rhuanjl]

I’m sorry I’ve been away and didn’t see this message, I’m not familiar with these errors, you may be trying to build with too new a windows RT or something. If you’re still interested, please can you try building with the ci build script?

Open a developer command line and run test/ci.buildone.cmd x64 test