How to use RegEx in Dart?

Question

In a Flutter application, I need to check if a string matches a specific RegEx. However, the RegEx I copied from the JavaScript version of the app always returns fa

Answer 1

This is a more general answer for future viewers.

Regex in Dart works much like other languages. You use the RegExp class to define a matching pattern. Then use hasMatch() to test the pattern on a string.

Examples

Alphanumeric

final alphanumeric = RegExp(r'^[a-zA-Z0-9]+$');
alphanumeric.hasMatch('abc123');  // true
alphanumeric.hasMatch('abc123%'); // false

Hex colors

RegExp hexColor = RegExp(r'^#?([0-9a-fA-F]{3}|[0-9a-fA-F]{6})$');
hexColor.hasMatch('#3b5');     // true
hexColor.hasMatch('#FF7723');  // true
hexColor.hasMatch('#000000z'); // false

Extracting text

final myString = '25F8..25FF    ; Common # Sm   [8] UPPER LEFT TRIANGLE';

// find a variable length hex value at the beginning of the line
final regexp = RegExp(r'^[0-9a-fA-F]+'); 

// find the first match though you could also do `allMatches`
final match = regexp.firstMatch(myString);

// group(0) is the full matched text
// if your regex had groups (using parentheses) then you could get the 
// text from them by using group(1), group(2), etc.
final matchedText = match.group(0);  // 25F8

There are some more examples here.