Question

I read some questions about this topic here at stackoverflow but none of them seems to answer my doubts.

I know how to create async functions using process.nextTick:

var async_function = function(val, callback){
    process.nextTick(function(){
        callback(val);
    });
};

I’ve also read about Promise, but how do you write async non-blocking functions without using libraries such as process, Promise, etc?

What’s the native way? I thought first on this approach:

var async = function(val, cb) {
    cb(val);    
}

However, that function blocks:

async(3, function(val) {
    console.log(val);
});
console.log(4);
// returns:
3
4

So what’s the correct implementation? How could I write async functions without depending on those libraries?

Answer 1

On Node.js, you need to be using process.nextTick. In the browser, you can use the postMessage hack which is much more efficient than setTimeout(function(){},0).

Here is a cross-browser implementation of the postMessage hack: https://github.com/timoxley/next-tick/blob/master/index.js