findLastIndex method
The findLastIndex method helps
to find the index of the first element
from the end of an array that matches
the condition according to the
callback
parameter. If there is no element, then
-1 is returned.
Syntax
array.findLastIndex(function);
Example
Let's find the index of a positive number in an array:
let arr = [-12, -13, 14, 15];
let res = arr.findLastIndex(function(elem) {
return elem > 0;
});
console.log(res);
The code execution result:
3
Example
And now let's find the index of an element that is not in an array:
let arr = ['a', 'b', 'c', 'd'];
let res = arr.findLastIndex(function(elem) {
return elem === 'f';
});
console.log(res);
The code execution result:
-1
