Callback function pattern

Functions are objects so they can be passed as arguments into other functions. It’s always recommended to check if passed parameter is a function.

In the example below getName is passed as an argument to sayHello function. Calling sayHello(getName) outputs “Hello Mike”.

function getName() {
    return 'Mike'
}

function sayHello(getName) {
	if (typeof getName === 'function') { // "function"
    	return `Hello ${getName()}` //Invoke function getName()
	} else {
		return console.log('Please pass a function');
    }
}

sayHello(getName) // "Hello Mike"
let name = "Brian";
sayHello(name) // "Please pass a function"

See the Pen Callback pattern by Mike (@mikemoney) on CodePen.