[Console] Fail to throw exception when output an undefined value

[xiaolongx]

If we only run console.log(a);, it will output JerryScript: cannot run javascript due to 'a' is undefined. But adding console.log(a) in setTimeout() and setInterval(), no exception thrown on both Arduino 101 and FRDM-K64F.

setTimeout(function() {
    console.log(a);
}, 1000);

But using the same code on chrome, it will throw exception like this:
Uncaught ReferenceError: a is not defined

Branch	Target Device	Build ID	Date	Result
master	Arduino	5a25755	Dec 21, 2016	Nothing Output
master	FRDM-K64F	5a25755	Dec 21, 2016	Nothing Output

[grgustaf]

Maybe this is a good thing. ;) Worth looking into, maybe we're squashing all exceptions somehow?

[jprestwo]

I do see this behavior, whether or not its a bug is up in the air. I think it could be a potential JerryScript issue. The reason that calling console.log(a) (not in setTimeout()) fails is because the JerryScript parser is catching it before execution. In the Timer module, functions get called later in the callback module. I looked in callbacks and we are checking to see if there was an error in execution of the callback function:

ret_val = jerry_call_function(cb_map[id]->js_func, cb_map[id]->this, data, sz);
if (jerry_value_has_error_flag(ret_val)) {
    DBG_PRINT("callback %d returned an error for function\n", id);
}

The question is, are we doing this correctly? I am not sure about that. This is how we do it everywhere else in the code, but perhaps this check won't catch syntax/parse/reference errors. The return value may just be related to errors thrown during runtime.

[jprestwo]

@grgustaf, can this be closed now that we added JS error printing to callbacks/main. Its the best we can do given the situation, since there is no way to actually throw an error (since its in the main loop).

[qiaojingx]

Verified with commit b29dbbc on Arduino 101.
Run: console.log(a);
Output:

src/main.c:228 main():                                                          
[ERROR] Error running javascript                                                
                                                                                
src/zjs_util.c:381 zjs_print_error_message():                                   
[ERROR] Uncaught exception: Error: 

Run:

setTimeout(function() {
    console.log(a);
}, 1000);

Output:

src/zjs_util.c:381 zjs_print_error_message():                                   
[ERROR] Uncaught exception: Error: 

[xiaolongx]

Closed since JS error printing is added to callbacks/main