Dynamic Imports: import() must produce a SyntaxError

[rwaldron]

While writing Test262 tests for dynamic import, I discovered the following incompatibility:

import()

Should produce a SyntaxError, given the grammar:

import ( AssignmentExpression )

Does not expand to import()

[fatcerberus]

This already appears to produce a SyntaxError.

// test.js
import();
print("This can't happen.");

Output

D:\temp>spherun test.js
miniSphere X.X.X JS game engine (x64)
a lightweight JavaScript-powered game engine
(c) 2015-2018 Fat Cerberus

GAME CRASH: error at '@/test.js':2:8
SyntaxError: Syntax error
   2 import();

[rwaldron]

Ok, I've narrowed it down further... this only happens when the -ESModule flag is present. Incidentally, that flag appears to cause other strangeness:

rwaldron in ~/js
$ echo "import();print('must not be reached');" >> dynamic-import.js
rwaldron in ~/js
$ cat dynamic-import.js
import();print('must not be reached');
rwaldron in ~/js
$ ch dynamic-import.js
SyntaxError: Syntax error
  at code (dynamic-import.js:1:7)
rwaldron in ~/js
$ ch -ESModule dynamic-import.js
rwaldron in ~/js

There's no output at all for ch -ESModule dynamic-import.js, which makes me think I might be doing something wrong here. I will close this for now and re-open if necessary.

[fatcerberus]

I see no change if I rename my test file to test.mjs (miniSphere will run it as a module), I still get a SyntaxError without reaching the print().

I think I see the problem though: ch -ESModule filename.js doesn't run the file as a module, it just enables module support while still loading the script as traditional code (I hit this pitfall myself in the past). You instead need to write a shim that does:

WScript.LoadScriptFile('module.mjs', 'module');  // execute root module

And then run the shim.

No idea why you get no output in that case though, that's kind of weird.

[rwaldron]

Lol, I just came back to post this same update. Thanks for preemptively confirming :D

[rhuanjl]

-ESModule isn't a flag that does anything in master.

-ESDynamicImport is the flag to enable import() - without it any dynamic import is a syntax error

[fatcerberus]

@rhuanjl Right, this issue was specifically about import() (with no specifier) incorrectly NOT being a syntax error; I’ve already verified that it is.