JavaScript: Passing parameters to a callback function

Question

Hi, I'm trying to pass some parameter to a function used as callback, how can I do that?

function tryMe (param1, param2) {
    alert (param1 + " and " + param2);
}

function callbackTester (callback, param1, param2) {
    callback (param1, param2);
}

callbackTester (tryMe, "hello", "goodbye");

Answer 1

If you want something slightly more general, you can use the arguments variable like so:

function tryMe (param1, param2) {
    alert(param1 + " and " + param2);
}

function callbackTester (callback) {
    callback (arguments[1], arguments[2]);
}

callbackTester (tryMe, "hello", "goodbye");

But otherwise, your example works fine (arguments[0] can be used in place of callback in the tester)

Answer 2

Your question is unclear. If you're asking how you can do this in a simpler way, you should take a look at the ECMAScript 5th edition method .bind(), which is a member of Function.prototype. Using it, you can do something like this:

function tryMe (param1, param2) {
    alert (param1 + " and " + param2);
}

function callbackTester (callback) {
    callback();
}

callbackTester(tryMe.bind(null, "hello", "goodbye"));

You can also use the following code, which adds the method if it isn't available in the current browser:

// From Prototype.js
if (!Function.prototype.bind) { // check if native implementation available
  Function.prototype.bind = function(){ 
    var fn = this, args = Array.prototype.slice.call(arguments),
        object = args.shift(); 
    return function(){ 
      return fn.apply(object, 
        args.concat(Array.prototype.slice.call(arguments))); 
    }; 
  };
}

Example

bind() - PrototypeJS Documentation

Answer 3

This would also work:

function tryMe (param1, param2) { 
    alert (param1 + " and " + param2); 
} 

function callbackTester (callback) { 
    callback(); 
} 

callbackTester (function() {tryMe("hello", "goodbye"); });