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

Why are you still using `co`? Just use `asnyc`/`await` syntax with promises. — Bergi, May 17 '18 at 06:20

score 0 · Accepted Answer · answered May 17 '18 at 02:44

Two issues:

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);
  });
};

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.

how to use co.wrap with generator

1 Answers1