The lastIndex property returns the character position where the last successful match begins in a searched string.
The lastIndex property is zero-based, that is, the index of the first character is zero. Its value is modified whenever a successful match is made.
The lastIndex property is modified by the exec and test methods of the RegExp object, and the match, replace, and split methods of the String object.
The following rules apply to values of lastIndex:
If there is no match, lastIndex is set to -1.
If lastIndex is greater than the length of the string, test and exec fail and lastIndex is set to -1.
If lastIndex is equal to the length of the string, the regular expression matches if the pattern matches the empty string. Otherwise, the match fails and lastIndex is reset to -1.
Otherwise, lastIndex is set to the next position following the most recent match.
