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;
}

Try it Yourself »

Definition and Usage

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.

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
A 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>