Med Java

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====== Java Script HOF (High Order Function) ======

(HOF) is a function that takes one or more functions as arguments and/or returns a function as its result. HOFs are a powerful feature in JavaScript and enable functional programming patterns. \\ 

A function qualifies as HOF if it does any of the following:

  * **Takes a function or more as an argument**: If a function accepts another function as a parameter, it's a HOF, even if it doesn't return a function itself.
  * **Returns a function**: If a function returns another function, it's also considered a HOF, even if it doesn't take a function as an argument.

===== Taking a function as an argument =====

<code javascript>
function runFunction(fn) {
  return fn();
}

function sayHello() {
  return 'Hello, world!';
}

const result = runFunction(sayHello);
console.log(result); // Outputs: Hello, world!
</code>

===== Returning a function =====

<code javascript>
function multiplier(factor) {
  return function(x) {
    return x * factor;
  };
}

const timesTwo = multiplier(2);
console.log(timesTwo(5)); // Outputs: 10
</code>

===== Both Taking a Function as an Argument and Returning a Function =====

<code javascript>
function compose(f, g) {
  return function(x) {
    return f(g(x));
  };
}

const addOne = x => x + 1;
const double = x => x * 2;

const addOneThenDouble = compose(double, addOne);

console.log(addOneThenDouble(2)); // Outputs: 6
</code>

<note tip>
Higher-order functions enable more abstract and concise code, promote reusability, and facilitate functional programming techniques like currying, partial application, and composition. \\ 
Functions like **map, filter, and reduce** are examples of built-in higher-order functions in JavaScript.
</note>

===== HOF vs Callback =====

A callback is a function that is passed as an argument to another function and is expected to be executed at some point in the future, either asynchronously or after some computation. \\ 
;;;Essentially, a callback is a specific instance of a function argument that a HOF might take.;;; \\ 
Example:
<code>
function fetchData(url, callback) {
  // Simulating an async operation
  setTimeout(() => {
    const data = "Some data from " + url;
    callback(data);
  }, 1000);
}

fetchData('http://example.com', (result) => {
  console.log(result);
});

</code>

In this example, the anonymous function passed as the second argument to **fetchData** is a **callback**. It gets executed after a timeout.


**HOF** refers to the concept of functions operating on other functions by taking them as arguments, returning them, or both.\\ \\ 

**Callback** refers to a specific function that is meant to be **executed at a later time or after some computation**, and is often passed to a **HOF**.

<note>
In other words, a callback is a type of argument that a higher-order function might accept. It is a pattern used for deferred or asynchronous operations. So, while all callbacks used in this way are an example of higher-order functions, not all higher-order functions are using callbacks for deferred or asynchronous execution.
</note>