Convert closure to es6 module

问题

I'm using a javascript build environment that supports es6 modules (using es6-module-transpiler) so you can simply import stuff across different files.

Now I got a third party library that I'd like to be "importable".

The library populates its functionality like this:

(function () {/*...*/}).call(this);

Would it be safe to omit the closure and convert it to:

export default function () {/* ... */};

Or is there a better way?

Thanks in advance!

回答1:

The original code you show invokes the anonymous function, which to make any sense must define a global variable, whereas the second code fragment you show merely exports the function, which is a different thing.

For purposes of discussion, let's assume the original code defines a global like this:

// my-third-party-module.js
(function() {
  let myVar = 22;
  window.MyThirdPartyModule = { log: function() { console.log(myVar); } };
}.call(this);

and you are using is as so:

// app.js
MyThirdPartyModule.log();

You could rewrite this as

// my-third-party-module.js
let myVar = 22;
export default { log: function() { console.log(myVar); } };

// app.js
import MyThirdPartyModule from `my-third-party-module';
MyThirdPartyModule.log();

Note that we have moved the variable myVar which was local to the anonymous function to the top module level.

However, depending on your preferences, rather than exporting a big object, which is sort of a pre-module mentality, you might want to export its APIs individually:

// my-third-party-module.js
let myVar = 22;
export function log { console.log(myVar); }

// app.js
import {log} from `my-third-party-module';
log();

or if you prefer

// app.js
import * as MyThirdPartyModule from `my-third-party-module';
MyThirdPartyModule.log();

However, all of these approaches assume you are able and willing to edit the source of the third party library. If that is not the case, you could write a little piece of glue code, such as

// my-third-party-module-interface.js
import 'my-third-party-module';    // This will run the module.
export default MyThirdPartyModule; // Export the global it defined.

// app.js
import MyThirdPartyModule from 'my-third-party-module-interface';

If you would prefer again to export individual APIs, you could extend the glue to re-export each of them:

// my-third-party-module-interface.js
import 'my-third-party-module';    // This will run the module.

const {log, otherAPI, ...} = MyThirdPartyModule;
export {log, otherAPI, ...};

// app.js
import {log} from 'my-third-party-module-interface';

回答2:

The conversion of legacy dependencies is still an issue. And the horrible workflow they use makes things a lot harder, prefixing the actual code with browserify and webpack silliness.

So what to do? Existentially, the library is guaranteed only to deposit a global in window but by obscure and weird ways. And all slightly different.

So let the legacy simply do what it is supposed to do for you, but wrapped in a module so that you can import it rather than use a script tag:

https://medium.com/@backspaces/es6-modules-part-2-libs-wrap-em-up-8715e116d690

来源：https://stackoverflow.com/questions/25840770/convert-closure-to-es6-module

标签

javascript

ecmascript-6

code-translation