1596058020

# What are Higher-Order Functions?

Though the term higher-order may sound fancy and complicated, it is actually much simpler than you’d think. In fact, you have probably already used higher-order functions without even realizing it.

`higher-order function` is a function that either takes a function or functions in as an argument or returns a function. All other types of functions are considered `first-order functions`. Because JavaScript accepts higher-order functions, that is what makes this programming language suitable for functional programming.

To better understand this concept, you first need to know a bit about functional programming and `first class functions`. Functional programming is a paradigm where you build applications with functions, as the name implies. This is accomplished with the use of pure functions, recursion and avoiding side-effects, mutable data, and shared state. If you want a more thorough explanation on functional programming, you can read my post about it here.

#javascript #functional-programming #higher-order-function

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## Higher-Order Functions Beginners Should Be Familiar With.

Higher-order functions are functions that operate on other functions, either by taking them as arguments or by returning them.

There are a lot more higher order functions than what will be covered in this article, but these are good ones to get you up and running as a beginner. These standard array methods are `forEach()` , `filter()` , `map()` and `sort()` .

1. **forEach( ): **This is used when you want to operate on or interact with any element inside of an array. Basically works like the_ for loop._

N.B- I’d be using examples to illustrate each method so you can get a clearer picture, and also just printing to the console to keep the examples as simple and basic as possible.

Example: Lets say in an array of a group or friends, and we want to loop through that array and print to the console each element of that array.

Using a for loop ;

``````const friends = ['Toyin', 'Olumide', 'Fola', 'Tola'];

for ( let i=0; i < friends.length ; i++) {
cosole.log (friends[i])
};
``````

The action same as above can be achieved using the`forEach()` method as seen below;

``````const friends =  ['Toyin', 'Olumide', 'Fola', 'Tola'];

friends.forEach(function(name) {
console.log(name)
};
``````

What the `forEach()` method simply does is to take in a function as an argument and loop through each item in the array without using iteration[i].

This is really awesome when the ES6 arrow functions are used, our code is reduced to a single line that is clean and maintainable. As seen below:

``````const friends =  ['Toyin', 'Olumide', 'Fola', 'Tola'];

friends.forEach(name => console.log (name));
``````

2. **_filter( ) : _**Just like the name implies, it is used to filter out elements of an array that do not meet the conditions set in the callback function passed as an argument. The callback function passed to the `filter()` method accepts 3 parameters: `element``index`, and `array` , but most times only the `element `parameter is used.

**Example : **In an array showing a group of friends and their ages, lets say we want to print to the console the friends that can drink assuming the age limit for drinking is 18. Using a for loop without high order functions;

``````const friends = [
{name : 'Toyin', age: 24},
{name : 'Olumide', age: 14},
{name : 'Fola', age: 12},
{name : 'David', age: 42}
];
for ( let i=0 ; i<friends.length ; i++) {
if (friends[i].age > 18) {
console.log(`\${friends[i].name} can drink`);
}
};
``````

Now using the `filter()` method :

``````const friends = [
{name : 'Toyin', age: 24},
{name : 'Olumide', age: 14},
{name : 'Fola', age: 12},
{name : 'David', age: 42}
];
friends.filter (function (friend) {
if (friend.age > 18){
return true;
}
});
``````

#functional-programming #beginners-guide #javascript #higher-order-function #es5-vs-es6 #function

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## Functional Programming: Higher Order Functions

A Better Take on JavaScript’s Higher Order Functions.

Functional Programming is awesome! It makes programming fun.

Learning to program “functionally” is going to make you a fantastic programmer and you will feel secure with the quality of your work.

You will be able to write your programs with fewer bugs and in less time because you will be able to re-use your code.

Within this paradigm, we will focus on one of the most important concepts in functional programming, and that is Higher-Order Functions.

So let’s get started!

In JavaScript, and in many functional programming languages, functions are values.

Let’s take a simple function for example:

``````function double(x) {
return x * 2
}
``````

What is super cool about JavaScript is that we can take this function and make it into an anonymous function to pass it around and re-use it by declaring a variable.

``````let double = function(x) {
return x * 2
}

let pancake = double
pancake(40) // 80
``````

We declared a variable _double _and assigned it to the anonymous function. Then we declared another variable, pancake, and assign it to the same function. Just like strings and numbers, functions too can be assigned to variables.

So, in functional programming, functions are values and they can be assigned to variables and they can also be passed into other functions.

Functions that operate on other functions, either by taking them as arguments or by returning them, are called higher-order functions. — see Eloquent JavaScript

In other words, as pertaining to our example, higher-order functions can be understood as functions being passed into other functions to do awesome things!!!

Sure, that makes sense, right? But what are these good for?

Composition.

The fact that we can take one function and put it into another function allows us to compose a lot of small functions into bigger functions.

Let’s look at how to use one of these higher-order functions. Probably the most basic and useful function is

# Filter( )

Filter() is a function on the array that accepts another function as its argument, which it will use to return a new filtered version of the array.

Let’s make a fun array of something.

``````const pets = [

{ name: 'Flip flop', species: 'rabbit' },
{ name: 'Dino', species: 'dog' },
{ name: 'Ralph', species: 'fish' },
{ name: 'Chuchi', species: 'cat' },
{ name: 'Ari', species: 'dog' },
{ name: 'Spock', species: 'dog' },
{ name: 'ying yang', species: 'cat' },
]
``````

What we want to do here is to just “filter” out all the dogs.

Our output must include Dino, Ari, and Spock. 😆

Question: How would I do this with a normal loop?

#higher-order-function #javascript #security #programming #code-review #function

1596058020

## What are Higher-Order Functions?

Though the term higher-order may sound fancy and complicated, it is actually much simpler than you’d think. In fact, you have probably already used higher-order functions without even realizing it.

`higher-order function` is a function that either takes a function or functions in as an argument or returns a function. All other types of functions are considered `first-order functions`. Because JavaScript accepts higher-order functions, that is what makes this programming language suitable for functional programming.

To better understand this concept, you first need to know a bit about functional programming and `first class functions`. Functional programming is a paradigm where you build applications with functions, as the name implies. This is accomplished with the use of pure functions, recursion and avoiding side-effects, mutable data, and shared state. If you want a more thorough explanation on functional programming, you can read my post about it here.

#javascript #functional-programming #higher-order-function

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## The Difference Between Regular Functions and Arrow Functions in JavaScript

Other then the syntactical differences. The main difference is the way the this keyword behaves? In an arrow function, the this keyword remains the same throughout the life-cycle of the function and is always bound to the value of this in the closest non-arrow parent function. Arrow functions can never be constructor functions so they can never be invoked with the new keyword. And they can never have duplicate named parameters like a regular function not using strict mode.

###### Here are a few code examples to show you some of the differences
```this.name = "Bob";
const person = {
name: “Jon”,
```<span style="color: #008000">// Regular function</span>
func1: <span style="color: #0000ff">function</span> () {
console.log(<span style="color: #0000ff">this</span>);
},

<span style="color: #008000">// Arrow function</span>
func2: () =&gt; {
console.log(<span style="color: #0000ff">this</span>);
}
```
}
person.func1(); // Call the Regular function
// Output: {name:“Jon”, func1:[Function: func1], func2:[Function: func2]}
person.func2(); // Call the Arrow function
// Output: {name:“Bob”}```

###### The new keyword with an arrow function
```const person = (name) => console.log("Your name is " + name);
const bob = new person("Bob");
// Uncaught TypeError: person is not a constructor```

###### If you want to see a visual presentation on the differences, then you can see the video below:

#arrow functions #javascript #regular functions #arrow functions vs normal functions #difference between functions and arrow functions

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## Higher Order Functions in JavaScript

Functional programming is a paradigm that results in cleaner and more concise code, that is easier to maintain, and reduces hard to find bugs. A central concept in functional programming is higher order functions. In JavaScript there a multiple of built in higher order functions.

According to Wikipedia a higher order function does one of the following:

• takes one or more functions as arguments (i.e. procedural parameters),
• returns a function as its result.

# Filter

Lets get to it. In enterprise grade software, we sometimes want to filter on cute dogs.

``````const dogs = [

{ name: 'Cocker spaniel', cute: true },
{ name: 'Chihuahua', cute: false },
{ name: 'Malteser', cute: true },
{ name: 'Tax', cute: false },
]
``````

We could use a for-loop for this. Where we would iterate over each dog and filter based on the cute boolean.

``````const cuteDogs = [];
for (let i = 0; i < dogs.length; i++) {
if (dogs[i].cute)
cuteDogs.push(dogs[i]);
}
``````

However there is a much simpler solution, that is more elegant, that is using the filter function.

``````const cuteDogs = dogs.filter(dog => dog.cute);
``````

#javascript #functional-programming #higher-order-function