JavaScript Array findIndex()

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Example 1

Find the first element with a value over 18:

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

ages.findIndex(checkAge);

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

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Description

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

The findIndex() method returns the index (position) of the first element that passes a test.

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

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

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

Array Find Methods:

Method	Finds
includes()	Returns true if an array contains a specified value
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.findIndex(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 first element that passes the test. Otherwise -1.

More Examples

Find the first 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.findIndex(checkValue);
}
</script>

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