Runtime is not strict mode compliant

[appden]

To reproduce: node --use_strict regenerator/runtime.js. This is a problem when compiling with 6to5, as it will automatically include the strict header.

Error Output

regenerator/runtime.js:318
        function next() {
        ^^^^^^^^
SyntaxError: In strict mode code, functions can only be declared at top level or immediately within another function.
    at Module._compile (module.js:439:25)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Function.Module.runMain (module.js:497:10)
    at startup (node.js:119:16)
    at node.js:929:3

Minor Performance Opportunity?

While on this topic, shouldn't the runtime include the "use strict" header so that it can take advantage of performance optimizations that v8 and other engines likely provide?

[sebmck]

@appden In what scenario does 6to5 include "use strict"; in the regenerator runtime?

[appden]

@sebmck This is not the default behavior, but happened as a result of my crazy build configuration to get my project packaged up correctly as a self-contained library. So yes, most users won't encounter this particular issue with 6to5.

[sebmck]

@appden Ah right okay. Just wanted to check if there were any potential bugs on our end.

[benjamn]

That particular problem is easy enough to fix, but I'm not sure what to do about the current technique of assigning to the undeclared regeneratorRuntime variable to make it global. It seems like that's not allowed in strict mode? If so, that's too bad, because it will be difficult to get a reference to the global object in a way that's CSP-compliant. Any ideas about that are welcome!

[sebmck]

Yeah, it's illegal to assign to undeclared variables in strict mode. A reliable way to get the current global scope (at least in my experience) has been typeof self === "undefined" ? global : self. self will support web workers, browsers etc while global will catch node, browserify etc.

[appden]

@benjamn thank you for fixing this so quickly!