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'
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