What does `return function *(){...}` mean? [duplicate]

Question

I saw something strange in Koa. It has some new function names (from https://github.com/koajs/koa/blob/master/examples/co.js#L10):

app.use(function(){   return function *(){     var paths = yield fs.readdir('docs');      var files = yield paths.map(function(path){       return fs.readFile('docs/' + path, 'utf8');     });      this.type = 'markdown';     this.body = files.join('');   } }); 

What does return function *() mean? Can we declare a function with the name of * in JavaScript?

Answer 1

It means that the function returns an iterator (so it can be repeatedly called with .next() to yield more values.

check out http://wingolog.org/archives/2013/05/08/generators-in-v8 for more info

It's an ES6 construct, so at the moment you see it more in node rather than client side js

Answer 2

Koa makes use of a new JavaScript feature called generators, and the * is the way to identify a generator in V8.