substr vs substring

Both substr and substring are common functions to get a sub-string of a given string.

Differences

1. Both methods have two parameters. The first parameters indicate the index of starting position of sub-string. The second parameters are different.

   substr(startPosition, length);
   substring(startPosition, endPosition);

   As you can see, the second parameters of substr and substring are the length and the end position of sub-string respectively. Given a string of helloworld:

   'helloworld'.substr(2, 4); // 'llow'
   'helloworld'.substring(2, 4); // 'll'

2. substr allows to use a negative number for the start position parameter.

   'helloworld'.substr(-2, 4); // 'ld'

   substring, on the other hand, will turn a negative start position to 0 (zero):

   'helloworld'.substring(-2, 5); // 'hello'
   'helloworld'.substring(0, 5); // 'hello'

Good to know

slice is another function for getting a sub-string. It's not deprecated as substr, and supports negative indices.

'helloworld'.slice(2, 4); // 'll'
'helloworld'.slice(-10, 5); // 'hello'
'helloworld'.slice(-5); // 'world'