babel 下循环引用 导致的import值为 undefined

[JoyMoch]

babel/babel#4094

That is to be expected, you have a circular dependency in your files

entry.js -> actions.js -> store.js -> actions.js

When store.js loads action.js, it is already in the queue, but hasn't executed yet because it is waiting for store.js to finish. Now because store.js depends on actions.js, but it is already loading, it will run store.js. The imported value actionTypes is undefined because actions.js hasn't executed yet.

In a real ES6 environment, this would throw a temporal deadzone error, but Babel does not support them in this case.

Your best bet would be to instead make store.js be:

export {actionTypes as default} from './actions';
so that the value is re-exported directly. This will take advantage of live bindings and avoids actually accessing the value of actionTypes until after actions has executed.

[JoyMoch]

debug 循环引用可以通过断点后的callstack往前看