带参数和返回值的Javascript回调

Question

Here is my dilemma, I have a series of functions that get called and I am using callbacks to execute a function when they are complete. The callback returns a value and that works great too, my problem is when I add parameters to the callback I can no longer access the returned value. Here is an example what works:

function myFunc1(x, y) {
   /*do stuff*/
   myFunc2(z, callback);
}

function callback(results) {
   alert(results);  /*this works!*/
}

This works great, the results returned are displayed. My problem what I need to do is something like this:

function myFunc1(x, y) {
   /*do stuff*/
   myFunc2(z, callback(x,y));
}

function callback(x,y,results) {
   alert(x);        /*works!*/
   alert(y);        /*works!*/
   alert(results);  /*doesn't work :(*/
}

I need a way to access both the value return as well as my parameters. Is something like this possible??

Answer 1

You can use Function.prototype.bind , like this

myFunc2(z, callback.bind(null, x, y));

bind function will return a new function with the first parameter as the context and the next parameters are the actual parameters passed to callback when invoked.

Answer 2

You will need to not call the callback immediately, but instead make a function that calls callback later with the expected arguments:

function myFunc1(x, y) {
    /*do stuff*/
    myFunc2(z, function(results) {
        callback(x, y, results);
    });
}

The .bind() variant proposed by @thefourtheye is basically ¹ a shortcut for this function expression.

_{1: rather for function(results) { return callback.call(null, x, y, results) } , also it would pass through more arguments than only results , and it would evaluate x and y at the time of the bind call.}