The Array findIndex() method executes a function for each array element, and returns the index (position) of the first element that passes a test.

<!-- html element to place output -->
<p id="my_ages"></p>

// array
let ages = [9, 23, 33, 43];

// function to run
function check_ages(age) {
    return age >= 18;
}

// output the index of the first item to meet the requirments of the function
document.getElementById('my_ages').innerHTML = 'Index: ' + ages.findIndex(check_ages);

The way this works (see Syntax section below):

• The find() method cycles through the array looking for the first item to pass the requirements of the function, and returns the index (position) of that item

1

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

Parameter	Description
function()	A function to be run for each element in the array (required)
currentValue	The value of the current element (required)
index	The index of the current element
arr	The array of the current element
thisValue	A value passed to the function as its "this" value (default is undefined)

---