Callbacks

• Define a callback function

• Demonstrate ability to pass a function as a parameter

Functions may seem very different than the other javascript items we've worked with before, but don't be fooled! Functions are still first-class values, which means you can

• store them in variables

• pass them as arguments to other functions

• create them within functions

• return them from functions

If this all seems very strange, you could think of a javascript function as a javascript object that stores code to be run instead of key/value pairs. A callback function is just a regular function that we pass as an argument to another function!

Take a look at this example:

function greeting() {
    console.log("Hello, World!");
}

function formalGreeting(informalGreeting) {
    informalGreeting();
    console.log("How are you?");
}

formalGreeting(greeting)

When we pass a function into another function as a paramenter, we are passing the function definition, so it can be called at a later time (hence the name callback). Notice the different outputs in the below example. First we print the function itself, then we call the function and print the output.

function returnRandom() {
    return (Math.random()*100).toFixed();
}

function yellRandom(randomNumGenerator) {
    console.log("GENERATOR DEFINITION: ", randomNumGenerator)
    console.log("YOUR RANDOM NUMBER IS: "+randomNumGenerator());
}

yellRandom(returnRandom)