Returns the position of the last match pattern in this string, searching backward starting at start, inclusive:
var string = 'Dartisans';
string.lastIndexOf('a'); // 6
string.lastIndexOf(new RegExp(r'a(r|n)')); // 6
Returns -1 if other could not be found.
string.lastIndexOf(new RegExp(r'DART')); // -1
start must not be negative or greater than length.