The Javascript arr.reduce() method in JavaScript is used to reduce the array to a single value and executes a provided function for each value of the array (from left to right) and the return value of the function is stored in an accumulator.
Syntax:
array.reduce( function(total, currentValue, currentIndex, arr),
initialValue )
Parameters:
This method accepts five parameters as mentioned above and described below:
-
function(total, currentValue, index, arr): It is the required parameter and is used to run for each element of the array. It contains four parameters which are listed below:
- total: It is a required parameter and is used to specify the initial value or the previously returned value of the function.
- currentValue: It is a required parameter and is used to specify the value of the current element.
- currentIndex: It is an optional parameter and is used to specify the array index of the current element.
- arr: It is an optional parameter and is used to specify the array object the current element belongs to.
- initialValue: It is an optional parameter and is used to specify the value to be passed to the function as the initial value.
Return value:
The JavaScript array reduce method returns a single value/element after traversing the complete array.
Below are examples of the Array reduce() method.
Example 1: In this example, we will write a reduce function to simply print the difference of the elements of the array.
// Input array let arr = [175, 50, 25]; // Callback function for reduce method function subofArray(total, num) {
return total - num;
} //Fucntion to execute reduce method function myGeeks(item) {
// Display output
console.log(arr.reduce(subofArray));
} myGeeks() |
100
Example 2: This example uses reduce() method to return the sum of all array elements.
// Input array let arr = [10, 20, 30, 40, 50, 60]; // Callback function for reduce method function sumofArray(sum, num) {
return sum + num;
} //Fucntion to execute reduce method function myGeeks(item) {
// Display output
console.log(arr.reduce(sumofArray));
} myGeeks(); |
210
Example 3: This example uses reduce() method to return the round sum of all array elements.
// Input array let arr = [1.5, 20.3, 11.1, 40.7]; // Callback function for reduce method function sumofArray(sum, num) {
return sum + Math.round(num);
} //Fucntion to execute reduce method function myGeeks(item) {
// Display output
console.log(arr.reduce(sumofArray, 0));
} myGeeks(); |
74
We have a complete list of Javascript Array methods, to check those please go through this Javascript Array Complete reference article.
Supported Browsers: The browsers supported by JavaScript Array reduce() method are listed below:
- Google Chrome
- Microsoft Edge
- Mozilla Firefox
- Safari
- Opera
We have a Cheat Sheet on Javascript where we covered all the important topics of Javascript to check those please go through Javascript Cheat Sheet-A Basic guide to JavaScript.