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JavaScript Array method: reduceRight()

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The reduceRight() method (when applied to a JavaScript array) reduces the values of an array to a single value (evaluating from right to left, i.e. from highest to lowest index).

 

It has the following syntax with the following parameters. It returns the accumulated result from the last call of the function. It does not execute the function if the array element does not have a value.

 

array.reduceRight(function(total, currentValue, index, arr), initialValue)

 

Parameter

Required / Optional

Description

function(total, currentValue, index, arr)

Required

A function to be run for each element

initialValue

Optional

A value to be passed to the function to be used as the initial value

 

The function arguments are:

 

Parameter

Required / Optional

Description

total

Required

The initalValue or the previously returned value of the function

currentValue

Required

The value of the current element

Index

Optional

The array index of the current element

arr

Optional

The array object which the current element belongs to

 

EXAMPLE:


HTML USED IN THIS EXAMPLE:
<!DOCTYPE html>
<html> <!-- Copyright (c) Nematrian Limited 2018 -->
<head>
<style>
table,th,tr,td {border: 1px solid black; border-collapse: collapse;}
</style>
</head>
<body>
<table>
<tr>
<th>Example</th>
<th>Resulting value of <code>x</code></th>
</tr>
<tr>
<td><code id="Example"></code></td>
<td><code id="Result"></code></td>
</tr>
</table>

<script>
var h = [1, 2, 3];
document.getElementById("Example").innerHTML =
  'var h = [1, 2, 3];<br>' +
  'function square(tot, x) {<br>' +
  '&nbsp;&nbsp;return tot + x * x;<br>' +
  '}<br>' +
  'var x = h.reduceRight(sumsquare, 5);';
document.getElementById("Result").innerHTML
  = h.reduceRight(sumsquare, 5);

function sumsquare(tot,x) {
  return tot + x * x;
}
</script>

</body>
</html>

FUNCTION THAT MAY ASSIST IN TESTING WHETHER FEATURE IS SUPPORTED:
function isSupportedJavaScriptMethodArrayReduceRight() {
  var h = [1, 2, 3]; return !!h.reduceRight;
}


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