revision:
The findLastIndex() method iterates the array in reverse order and returns the index of the first element that satisfies the provided testing function. If no elements satisfy the testing function, -1 is returned.
findLastIndex(callbackFn)
findLastIndex(callbackFn, thisArg)
Parameters:
callbackFn : 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 : the current element being processed in the array.
index : the index of the current element being processed in the array.
array : the array findLastIndex() was called upon.
thisArg : optional. A value to use as "this" when executing callbackFn.
const array1 = [5, 12, 50, 130, 44];
const isLargeNumber = (element) => element > 45;
console.log(array1.findLastIndex(isLargeNumber));
// Expected output: 3
// Index of element with value: 130
The lastIndexOf() method returns the index (position) of the last occurrence of a specified value in a string. The lastIndexOf() method searches the string from the end to the beginning. It returns the index from the beginning (position 0). It returns -1 if the value is not found. The lastIndexOf() method is case sensitive.
string.lastIndexOf(searchvalue, start)
Parameters:
searchvalue : required. The string to search for.
start : optional. The position where to start. Default value is string length.
<p id="demo"></p>
let text = "Hello planet earth, you are a great planet.";
let result = text.lastIndexOf("planet");
document.getElementById("demo").innerHTML = result;
example: fid the index of the last prime number in an array.
<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, 12].findLastIndex(isPrime)); // -1, not found
console.log([4, 5, 7, 8, 9, 11, 12].findLastIndex(isPrime)); // 5
document.getElementById("find-1").innerHTML = "last Prime in the array? " + [4, 6, 8, 12].findLastIndex(isPrime);
document.getElementById("find-2").innerHTML = "last Prime in the array? " + [4, 5, 7, 8, 9, 11, 12].findLastIndex(isPrime);
</script>
example: search for the last occurence of "planet".
<div>
<p id="find-3"></p>
<p id="find-4"></p>
</div>
<script>
let text = "Hello planet earth, you are a great planet.";
let result = text.lastIndexOf("Planet");
let result1 = text.lastIndexOf("planet");
document.getElementById("find-3").innerHTML = "last index of 'Planet' : " + result;
document.getElementById("find-4").innerHTML = "last index of 'planet' : " + result1;
</script>
example: find the last position of "planet", starting at position 29.
<div>
<p id="find-5"></p>
<p id="find-6"></p>
</div>
<script>
let text2 = "Hello planet earth, you are a great planet.";
let result2 = text.lastIndexOf("planet", 20);
document.getElementById("find-5").innerHTML = "last occurence of 'planet' from position 20 : " + result2;
</script>