Can anyone show me how to write a simple javascript/Node.js hook(add pre and post to (async)function)?

[赵正中]

Hi,

I'm a Node.js newbie

Can anyone show me how to write a simple javascript/Node.js hook(add pre and post to (async)function)?

So far, I've checked

Javascript function hooks

https://github.com/cowboy/javascript-hooker

https://github.com/bnoguchi/hooks-js

But I have hard time to understand the code, can anyone help?

Thank you!

[alessioalex]

Hey,

So async functions look like the following:

  asyncFn(param1, param2, ..., callback);

The callback should be the last argument. That means you can override an async function to call your pre hook before it gets executed and also override the callback so that the hook gets executed after the it.

For example:

  hookify = function(originalFn, preFn, afterFn) {

    var fn = originalFn;

    originalFn = function() {

      var args = Array.prototype.slice.call(arguments);

      // the callback is the last argument; we also delete it from the args array this way

      var originalCallback = args.pop();

      // override the callback so that it calls the after hook

      var callback = function() {

        originalCallback.apply(this, arguments); 

        afterFn();

      };

      // put in the args array again, as the last item    

      args.push(callback);

      // call the pre hook

      preFn();

            

      // execute original function

      fn.apply(this, args);

    };

  };

So then you can just use it this way:

  hookify(asyncFn, function() {

    console.log('pre hook');

  }, function() {

    console.log('post hook');

  });

  asyncFn(1, 2, 3, function() {

    console.log('callback');

  });

That should log:

  pre hook

  callback

  post hook

Note: I haven't tested that function, but that's the principle.

Let me know if that clarifies it for you.

Best,

Alex