如何与生成器一起使用co.wrap

Question

const co = require('co');

const func1 = function(){
  setTimeout(()=>{
    console.log('func1');
  },2000);
}

const func2 = function(){
  setTimeout(()=>{
    console.log('func2');
  },2000);
}

const func3 = function(){
    console.log('func3');
}

const gen = co.wrap(function*(){
  yield func1;
  yield func2;
  return yield func3;
});


gen()
.then(function(){console.log('end')});

The expected result is func1 func2 func3 end

but it doesn't show what I intended.

It is showing func1

How can I fix the code to output the expected result

Answer 1

Two issues:

1. There's no way for your functions to return control. If you want to use thunks (which the documentation advises against), you need to actually take and invoke a callback:

    const func1 = function(cb){ setTimeout(()=>{ console.log('func1'); return cb(); },2000); }; 

   However, it's better to use promises:

    const func2 = function(){ return new Promise((resolve) => { setTimeout(()=>{ console.log('func2'); return resolve(); },2000); }); }; 

2. If you use promises, you need to invoke the function when you yield it:

    yield func2(); 

   You can only yield a function without calling it if it's a thunk.