What is the difference between substr and substring?

What is the difference between substr and substring?

What is the difference between
alert(“abc”.substr(0,2));

and
alert(“abc”.substring(0,2));

They both seem to output “ab”.

Solutions/Answers:

Solution 1:

The difference is in the second argument. The second argument to substring is the index to stop at (but not include), but the second argument to substr is the maximum length to return.

Links?

https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/String/substr

https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/String/substring

Solution 2:

substr (MDN) takes parameters as (from, length).
substring (MDN) takes parameters as (from, to).

alert("abc".substr(1,2)); // returns "bc"
alert("abc".substring(1,2)); // returns "b"

You can remember substring takes indices, as does yet another string extraction method, slice.

When starting from 0 you can use either method.

Solution 3:

As hinted at in yatima2975’s answer, there is an additional difference:

substr() accepts a negative starting position as an offset from the end of the string. substring() does not.

From MDN:

If start is negative, substr() uses it as a character index from the
end of the string.

So to sum up the functional differences:

substring(begin-offset, end-offset-exclusive) where begin-offset is 0 or greater

substr(begin-offset, length) where begin-offset may also be negative

Solution 4:

Another gotcha I recently came across is that in IE 8, "abcd".substr(-1) erroneously returns "abcd", whereas Firefox 3.6 returns "d" as it should. slice works correctly on both.

More on this topic can be found here.

Solution 5:

The main difference is that

substr() allows you to specify the maximum length to return

substring() allows you to specify the indices and the second argument is NOT inclusive

There are some additional subtleties between substr() and substring() such as the handling of equal arguments and negative arguments. Also note substring() and slice() are similar but not always the same.

  //*** length vs indices:
    "string".substring(2,4);  // "ri"   (start, end) indices / second value is NOT inclusive
    "string".substr(2,4);     // "ring" (start, length) length is the maximum length to return
    "string".slice(2,4);      // "ri"   (start, end) indices / second value is NOT inclusive

  //*** watch out for substring swap:
    "string".substring(3,2);  // "r"    (swaps the larger and the smaller number)
    "string".substr(3,2);     // "in"
    "string".slice(3,2);      // ""     (just returns "")

  //*** negative second argument:
    "string".substring(2,-4); // "st"   (converts negative numbers to 0, then swaps first and second position)
    "string".substr(2,-4);    // ""
    "string".slice(2,-4);     // ""

  //*** negative first argument:
    "string".substring(-3);   // "string"        
    "string".substr(-3);      // "ing"  (read from end of string)
    "string".slice(-3);       // "ing"        

Solution 6:

The difference is second parameter. Their second parameters, while both numbers, are expecting two different things:

When using substring the second parameter is the first index not to include:

var s = "string";
s.substring(1, 3); // would return 'tr'

var s = "another example";
s.substring(3, 7); // would return 'ther'

When using substr the second parameter is the number of characters to include in the substring:

var s = "string";
s.substr(1, 3); // would return 'tri'

var s = "another example";
s.substr(3, 7); // would return 'ther ex'