Slice and substring and substr

SUBSTR (begin,end): Begin indicates that the starting index,end means extracting several

SUBSTRING (begin,end): Begin indicates that the start index,end represents the end of index.

Slice (begin,end): with substring.

The difference between slice and substring:

1, substring 2 parameters if begin is greater than end, the position is exchanged; Slice will not be exchanged, return empty string directly

2, substring 2 parameters if negative, then automatically turn to 0;slice will say str.length plus its negative value to get is a few is a few

Slice and substring and substr