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Welcome to the Javascript-higher-order-functions- wiki!

_{This repository is part of a larger project!}

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Higher-order functions are functions which take as arguments another functions or return functions as their result. The functions given as arguments are known as callback functions. A simple example could be as follows:

function mainFunction(a, b, callback)
{
    var result = callback(a, b);
	
    return result; 
}

function callbackFunction(x, y)
{
   return x * y;
}

//Call - "callbackFunction" is not executed in the parameter 
//and will be called later within "mainFunction"
console.log(mainFunction(2, 2, callbackFunction));//Outputs 4

One thing which is important to understand is that callbackFunction could be defined differently (e.g. return x + y) and it will still work fine. Following this insight, High-order functions give the developer a certain flexibility to change or write callback functions as they need it whithin a specific frame.

Another way is to write a callback function as an anonymous function, like this:

function mainFunction(a, b, callback)
{
    var result = callback(a, b);
	
    return result; 
}

//a = 2 and b = 2
var output = mainFunction
(
	2,
	2,
	function(x,y)
	{
		return x * y;
	}

)

console.log(output)//Outputs 4

The anonymous version could be often seen in jQuery.

Javascript offers already useful Higher-order functions. The following functions listed are used in this project:

1. forEach()
2. map()
3. filter()
4. reduce()
5. reduceRight()
6. sort()

The first five ( sort() excluded ) have some parameters in common which could be used in a callback function:

• currentValue : Gives access to the current value in an array
• index : Gives access to the index for the current value in an array
• array : The array which is processed by the High-order function

Content

The user interaction part should look like the content as seen below by starting "index.html" in a web browser.

The user input seen in the picture above is the one which is used for all examples.

• 🅱️ utton "FOREACH": Shows all elements and the specific index of user input
• 🅱️ utton "MAP": Calculates the square of the unicode values which is extracted by separating characters
• 🅱️ utton "FILTER": Filters all chracters which unicode values difference is smaller than zero - the calculation is done with the next right neighbour character
• 🅱️ utton "REDUCE": Calculates the product of all unicode values of user input
• 🅱️ utton "REDUCE RIGHT": Reverse the user input
• 🅱️ utton "SORT": Sorts the user inputs characters from lowest to highest value

The colored areas are just for a better readability in the wiki and are not part of the content. To use the project just download the files and execute "index.html". Note that all files should be placed in the same folder so that the functionality of the code is guaranteed.