Pass a JavaScript function as parameter

Question

How do I pass a function as a parameter without the function executing in the \"parent\" function or using eval()? (Since I\'ve read that it\'s insecure.)

Answer 1

If you want to pass a function, just reference it by name without the parentheses:

function foo(x) {
    alert(x);
}
function bar(func) {
    func("Hello World!");
}

//alerts "Hello World!"
bar(foo);

But sometimes you might want to pass a function with arguments included, but not have it called until the callback is invoked. To do this, when calling it, just wrap it in an anonymous function, like this:

function foo(x) {
   alert(x);
}
function bar(func) {
   func();
}

//alerts "Hello World!" (from within bar AFTER being passed)
bar(function(){ foo("Hello World!") });

If you prefer, you could also use the apply function and have a third parameter that is an array of the arguments, like such:

function eat(food1, food2)
{
    alert("I like to eat " + food1 + " and " + food2 );
}
function myFunc(callback, args)
{
    //do stuff
    //...
    //execute callback when finished
    callback.apply(this, args);
}

//alerts "I like to eat pickles and peanut butter"
myFunc(eat, ["pickles", "peanut butter"]);