JavaScript | Array reduce() Method
The array 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 )
Parameter: This method accepts two parameters as mentioned above and described below:
- function(total, currentValue, index, arr): It is the required parameter and used to run for each element of array. It contains four parameter which are listed below:
- total: It is required parameter and used to specify the initialValue, or the previously returned value of the function.
- currentValue: It is required parameter and used to specify the value of the current element.
- currentIndex: It is optional parameter and used to specify the array index of the current element.
- arr: It is optional parameter and used to specify the array object the current element belongs to.
- initialValue: It is optional parameter and used to specify the value to be passed to the function as the initial value.
Example 1: This example use reduce() method to return the sum of all array elements.
<!DOCTYPE html> <html> <head> <title> JavaScript Array reduce() Method </title> </head> <body style="text-align:center;"> <h2>GeeksForGeeks</h2> <p> Click here to get the sum of array elements </p> <button onclick="myGeeks()"> Click Here! </button> <br><br> Sum: <span id="GFG"></span> <!-- Script to use reduce method --> <script> var arr = [10, 20, 30, 40, 50, 60]; function sumofArray(sum, num) { return sum + num; } function myGeeks(item) { document.getElementById("GFG").innerHTML = arr.reduce(sumofArray); } </script> </body> </html> |
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Output:
Before click on the button:
After click on the button:
Example 2: This example use reduce() method to return the round sum of all array elements.
<!DOCTYPE html> <html> <head> <title> JavaScript Array reduce() Method </title> </head> <body style="text-align:center;"> <h2>GeeksForGeeks</h2> <p> Click here to get the sum of array elements </p> <button onclick="myGeeks()"> Click Here! </button> <br><br> Sum: <span id="GFG"></span> <!-- Script to use reduce method --> <script> var arr = [1.5, 20.3, 11.1, 40.7]; function sumofArray(sum, num) { return sum + Math.round(num); } function myGeeks(item) { document.getElementById("GFG").innerHTML = arr.reduce(sumofArray, 0); } </script> </body> </html> |
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Output:
Before click on the button:
After click on the button:
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