trim abstract method

The string without any leading and trailing whitespace.

If the string contains leading or trailing whitespace, a new string with no leading and no trailing whitespace is returned:

final trimmed = '\tDart is fun\n'.trim();
print(trimmed); // 'Dart is fun'

Otherwise, the original string itself is returned:

const string1 = 'Dart';
final string2 = string1.trim(); // 'Dart'
print(identical(string1, string2)); // true

Whitespace is defined by the Unicode White_Space property (as defined in version 6.2 or later) and the BOM character, 0xFEFF.

Here is the list of trimmed characters according to Unicode version 6.3:

    0009..000D    ; White_Space # Cc   <control-0009>..<control-000D>
    0020          ; White_Space # Zs   SPACE
    0085          ; White_Space # Cc   <control-0085>
    00A0          ; White_Space # Zs   NO-BREAK SPACE
    1680          ; White_Space # Zs   OGHAM SPACE MARK
    2000..200A    ; White_Space # Zs   EN QUAD..HAIR SPACE
    2028          ; White_Space # Zl   LINE SEPARATOR
    2029          ; White_Space # Zp   PARAGRAPH SEPARATOR
    202F          ; White_Space # Zs   NARROW NO-BREAK SPACE
    205F          ; White_Space # Zs   MEDIUM MATHEMATICAL SPACE
    3000          ; White_Space # Zs   IDEOGRAPHIC SPACE

    FEFF          ; BOM                ZERO WIDTH NO_BREAK SPACE

Some later versions of Unicode do not include U+0085 as a whitespace character. Whether it is trimmed depends on the Unicode version used by the system.