revision:
The findIndex() method returns the index of the first element in an array that satisfies the provided testing function. If no elements satisfy the testing function, -1 is returned.
The findIndex() method executes a function for each array element and returns the index (position) of the first element that passes a test. The method returns -1 if no match is found. It does not execute the function for empty array elements and does not change the original array.
array.findIndex(callbackFn)
array.findIndex(callbackFn, thisArg)
array.findIndex(function(currentValue, index, arr), thisValue)
Parameters:
callbackFn, function : required; a function to execute for each element in the array. It should return a truthy value to indicate a matching element has been found, and a falsy value otherwise. The function is called with the following arguments:
element, currentValue : the (value of the) current element being processed in the array.
index : optional; the index of the current element being processed in the array.
array : optional; the array "findIndex()" was called upon.
thisArg, thisValue : optional. A value to use as "this" when executing callbackFn. Default "undefined".
const array1 = [5, 12, 8, 130, 44];
const isLargeNumber = (element) => element > 13;
console.log(array1.findIndex(isLargeNumber));
// Expected output: 3
<div>
<p id="find-1"></p>
<p id="find-2"></p>
</div>
<script>
function isPrime(element) {
if (element % 2 === 0 || element < 2) {
return false;
}
for (let factor = 3; factor <= Math.sqrt(element); factor += 2) {
if (element % factor === 0) {
return false;
}
}
return true;
}
console.log([4, 6, 8, 9, 12].findIndex(isPrime)); // -1, not found
console.log([4, 6, 7, 9, 12].findIndex(isPrime)); // 2 (array[2] is 7)
document.getElementById("find-1").innerHTML = "is there a Prime in the array? " + [4, 6, 8, 9, 12].findIndex(isPrime);
document.getElementById("find-2").innerHTML = "is there a Prime in the array? " + [4, 6, 7, 9, 12].findIndex(isPrime);
</script>
<div>
<p id="find-3"></p>
<p id="find-4"></p>
</div>
<script>
const ages = [3, 10, 18, 20];
document.getElementById("find-3").innerHTML = "original array : " + ages;
document.getElementById("find-4").innerHTML = "index of first element with value over 18 : " + ages.findIndex(checkAge);
function checkAge(age) {
return age > 18;
}
</script>
<div>
<p><input type="number" id="toCheck" value="18"></p>
<button onclick="findFunction()">Test</button>
<p id="find-5"></p>
<p id="find-6"></p>
</div>
<script>
const numbers = [4, 12, 16, 20];
function checkValue(x) {
return x > document.getElementById("toCheck").value;
}
function findFunction() {
document.getElementById("find-5").innerHTML = "value of first element above this input: " + numbers.findIndex(checkValue);
}
</script>