A simple extension for currency format on string in Dart

Hello this in my first article in english language and very sorry for my bad english writing.

in this article i want to share my experience in add currency format to string without package

void main() {
  print("1000".currency());
  print("1300000".currency());
  print("1005000".currency(symbol: '£'));
  print("1000000".currency(symbol: '€'));
}
extension StringFormatter on String{
  String currency({String symbol = "\$"}) {
  
    int step = 1;
    String val = this;
    
    for (var i = val.length-1; i >=0; i--) {
      if (i - 2*step > 0) {
        
        val = val.replaceRange(i-2*step, i-2*step, ",");
        step++;
      }
    }
    
    return "$symbol$val";
  }
}

Result

extension in dart is a feature that help you to add functions to other class that you don’t write it. and in here i am write extension for String class

Okay lets go to explain the code:

we have for loop from end to start of our string because splitter for currency start from write of price

we need to add character every 3 char for example: “,”
I used replaceRange method to insert character in special index.

How to find correct index to insert character? I am consider a variable for step that initial with 1. okay we need to check if we back 3 char before is grater than 0 and if true we can insert symbol each 3 char.
if we wanna for example 4 char it just need to replace 2 with 3 and

Done!