To find last index of element inside array by certain condition with JavaScript, we use the map and lastIndexOf methods.
For instance, we write
const lastIndex = elements.map((e) => e.a).lastIndexOf("something");
to call map with a callback that returns property a‘s value in each object e in elements.
Then we call lastIndexOf to get the last index of the a value that equals 'something' in the returned array.
