JavaScript Array reduce() Method
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 used to specify the initialValue 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.
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.
html
<body style="text-align:center;"> <h1 style="color: green;"> GeeksforGeeks </h1> <p> Click here to get the Subtract of array elements from the left side </p> <button onclick="myGeeks()"> Click Here! </button> <br><br> Subtract: <span id="GFG"></span> <!-- Script to use reduce method --> <script> var arr = [175, 50, 25]; function subofArray(total, num) { return total - num; } function myGeeks(item) { document.getElementById("GFG").innerHTML = arr.reduce(subofArray); } </script></body> |
Output:
Example 2: This example uses reduce() method to return the sum of all array elements.
html
<body style="text-align:center;"> <h1 style="color: green;"> GeeksforGeeks </h1> <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> |
Output:
Example 3: This example uses reduce() method to return the round sum of all array elements.
html
<body style="text-align:center;"> <h1 style="color: green;"> GeeksforGeeks </h1> <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> |
Output:
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 3 and above
- Microsoft Edge 12 and above
- Mozilla Firefox 3.0 and above
- Safari 5 and above
- Opera 10.5 and above
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.
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