JavaScript Fundamentals: Reduce

Aphinya Dechalert -

Javascript's reduce function is one of the most powerful tools in the language. It can be used to simplify a wide variety of tasks, including counting, summing, and averaging.

We use reduce because it is a fast and efficient way to iterate over an array and perform a certain operation on each element in the array. For example, we could use reduce to sum up all the numbers in an array, or to find the average of all the numbers in an array.

But what exactly is reduce in JavaScript?


Reduce is used to apply a function to each element in an array and reduce the array to a single value.

The reduce function takes two arguments:

  • a callback function
  • and an initial value.

The callback function takes two arguments:

  • the previous value
  • and the current value.

It returns a single value, which is passed to the next invocation of the callback function.

Pros and cons of using reduce in JavaScript

Reduce is a higher-order function that takes a function and an array as arguments and returns a single value generated by calling the function on each element of the array. A higher order function is a function that can take another function as an argument, and can also return a function as a result.

The main advantage of using reduce is that it can be used to perform operations on data structures that are not easily iterated over, such as trees. Additionally, reduce can be used to generate values that are not easily calculated, such as averages and sums.

A disadvantage of using reduce is that it can be difficult to understand the code, especially if the function is complex. Additionally, reduce can be slow if the array is large.

Example of how to use reduce

Suppose we have an array of numbers:

var numbers = [1, 2, 3, 4, 5];

We can use the reduce function to sum them:

var sum = numbers.reduce(function(prev, curr) {
  return prev + curr;
}, 0);

console.log(sum); // 15


We can also use reduce to count the number of elements in the array:

var count = numbers.reduce(function(prev, curr) {
  return prev + 1;
}, 0);

console.log(count); // 5

Similarly, we can use reduce to compute the average of the numbers in the array:

var average = numbers.reduce(function(prev, curr) {
  return (prev + curr) / 2;
}, 0);

console.log(average); // 3

As you can see, the reduce function is a powerful tool that can be used to simplify a wide variety of tasks. Give it a try the next time you need to perform a calculation on an array of data.