Node.js中的Hook函数调用

Question

is there a way to hook function call or redefine a function before a call in node.js? I need this for unit testing, may be Proxy or some testing libary is and option?

Example:

//some js file
function a(){
 b()// need to be hooked
} 

function b(){
  //do some stuff
}

Answer 1

What you can do is create a wrapper around the target function, and perform whatever operations you need to do before execution, ex:

const tmp = b
function b {
  doSomething()
  maybeBroadcastAnEvent()
  tmp() //run original function
}

Answer 2

You can use .apply() with the arguments object to forward the call data of a into the b function.

function a(){
 return b.apply(this, arguments)
} 

function b(){
  //do some stuff
}

So whatever this value and arguments were given to a will be forwarded to b , and whatever b returns will be returned by a .

---

As it seems you attempted in your newer question, you can create a function that binds b to the Function.prototype.call method to accomplish this more succinctly.

var a = Function.call.bind(b);

function b(){
  //do some stuff
}

Now when a is invoked, the first argument provided will become the this value of b and the rest of the arguments provided will become the regular arguments of b .

---

If you don't care about the this value, and just want to pass on all the args, you can bind null as the first argument to .call , so that b will just get forwarded all the provided arguments as regular args.

var a = Function.call.bind(b, null);

function b(){
  //do some stuff
}