JavaScript Array findLastIndex()

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Example 1

Find the last element with a value over 18:

const ages = [3, 10, 18, 20];

ages.findLastIndex(checkAge);

function checkAge(age) {
return age > 18;
}

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Description

The findLastIndex() method executes a function for each array element.

The findLastIndex() method returns the index (position) of the last element that passes a test.

The findLastIndex() method returns -1 if no match is found.

The findLastIndex() method does not execute the function for empty array elements.

The findLastIndex() method does not change the original array.

Array Find Methods:

Method	Finds
indexOf()	The index of the first element with a specified value
lastIndexOf()	The index of the last element with a specified value
find()	The value of the first element that passes a test
findIndex()	The index of the first element that passes a test
findLast()	The value of the last element that passes a test
findLastIndex()	The index of the last element that passes a test

Syntax

array.findLastIndex(function(currentValue, index, arr), thisValue)

Parameters

Parameter	Description
function()	Required. A function to be run for each array element.
currentValue	Required. The value of the current element.
index	Optional. The index of the current element.
arr	Optional. The array of the current element.
thisValue	Optional. Default `undefined`. A value passed to the function as its `this` value.

Return Value

Type	Description
Number	The index of the last element that passes the test. Otherwise -1.

More Examples

Find the last element with a value above an input value:

<p><input type="number" id="toCheck" value="18"></p>

<button onclick="myFunction()">Test</button>

<p>Any values above: <span id="demo"></span></p>

<script>
const numbers = [4, 12, 16, 20];

function checkValue(x) {
return x > document.getElementById("toCheck").value;
}

function myFunction() {
document.getElementById("demo").innerHTML = numbers.findLastIndex(checkValue);
}
</script>

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