Substr in js, the substring, indexOf, the use of the lastIndexOf etc

1. The substr Substr (start,length) intercepts a string of length from the start position.

Var SRC = “images/off_1. PNG”; Alert (SRC) substr (7, 3));

The pop-up value is: off  

2. The substring Substring (start,end) represents the string from start to end, including the character of the start position but not the character of the end position.

Var SRC = “images/off_1. PNG”; Alert (SRC. The substring (7, 10));

The pop-up value is: off

3. The indexOF The indexOf() method returns the first occurrence (from left to right) of a specified string value in a string. Returns -1 if there is no match, otherwise returns the lower value of the string at the first occurrence.

Var SRC = “images/off_1. PNG”; Alert (SRC) indexOf (’ t ’)); Alert (SRC) indexOf (’ I ’)); Alert (SRC) indexOf (” g ”));

The popup values are in order: -1,0,3

4. The lastIndexOf The lastIndexOf() method returns the index value of the first character of a character or string that appears from right to left (as opposed to indexOf)

Var SRC = “images/off_1. PNG”; Alert (SRC) lastIndexOf (’/’)); Alert (SRC) lastIndexOf (” g ”));

The pop-up values are, in order, 6,15