substr vs substring

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

Differences

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'
```
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'

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