week 3

 functions and an introduction to higher-order functions

Functions Review

Introduction to Higher Order Functions

Overview

Functions

function declaration, function expression and Anonymous Functions 

function declaration

function square (x) {
  return x * x;
};

A Function Declaration defines a named function without requiring var keyword

function expression

var square = function (x) {
  return x * x;
};

A Function Expression defines a function as a part of a larger expression syntax (typically a variable assignment )

Anonymous Functions

function (num1, num2) {
    return num1 + num2;
};

The function name. Can be omitted, in which case the function is anonymous.

Anonymous Functions

(function (num1, num2) {
    return num1 + num2;
})();

Invocation: wrap your function in an IIFE (immediately invoked function EXPRESSION)

Anonymous Functions

(function (num1, num2) {
    return num1 + num2;
})();

Usage: anonymous functions can only be called once

Anonymous Functions

(function (num1, num2) {
    return num1 + num2;
})();

Would this ever be helpful?

Higher Order Functions

Definition:

A function that takes another function

in as a PARAMETER

The function passed in as a parameter is called a CALLBACK

Higher Order Functions

each

//loops through an array 
//and invokes a callback on each element

function each (arr, callback){
  for(var i = 0: i < arr.length; i++){
    callback(arr[i]);
  }
};

Higher Order Functions

Example: each

function each (arr, callback){
    for (var i = 0; i < arr.length; i++){
        callback(arr[i]);
    }
};
// prints an element to the console
var print = function(element){
    console.log(element);
};

Higher Order Functions

Identifying the Callback

var arr = ['hi', 'my', 'name', 'is', 'albrey'];

each(arr, print);
// hi
// my
// name
// is
// albrey

callback!

higher order function

Higher Order Functions

Converting to an Anonymous Function

var arr = ['hi', 'my', 'name', 'is', 'albrey'];

each(arr, function(element) {
    console.log(element);
});

// hi
// my
// name
// is
// albrey