how to use co.wrap with generator

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.