Javascript Higher Order Functions

For a function to be considered a Higher Order Function it has to either accept a function as an argument or return a function. I will be discussing the Map, Filter, and Reduce functions in JavaScript because I have found they are the most useful. All three of these functions are called on array instances and manipulate the data in different ways. I will discuss what each function does and give an example of how to use each function.

The first function I will talk about is Map. The Map function iterates over the array it is called on and executes the callback function on each element. When the Map function is complete it returns a new array with the changes made in callback function incorporated. The callback function has one parameter that will hold the value of each element during the iteration.

The second function I will be discussing is the Filter function. Like Map, the Filter function is called on an array, but instead of changing each element in the array it passed the element into the callback function. After the iteration is complete the Filter function returns an array containing only the elements that returned true when passed into the callback function. The Filter function callback has one parameter that holds the value of the array element during the iteration.

The final function I will discuss is the Reduce function. Reduce does exactly what it sounds like, it reduces the array into a new value one element at a time. Reduce can take in up to four parameters, but the only mandatory parameters are an accumulator that will store the value that is returned and a variable for the array element being iterated over. The two optional parameters are an initial value to start the accumulator at, and a parameter to hold the index value of the current element which is useful if you want to do something special at the end.

These functions are very useful and are a great alternative to sandwich coding and using simple for loops. Using higher order functions are a great way to refactor your code and make it more efficient. Using Higher Order Functions will also show anyone who looks at your code that you have a advanced understanding of JavaScript.

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