Why AngularJS currency filter formats negative numbers with parenthesis?

Question

Live Demo

Why this:

# Controller
$scope.price = -10;

# View
{{ price | currency }}

results in ($10.00) rather than

Answer 1

It works better for me by checking negative number:

var app = angular.module('myApp');

app.filter('customCurrency', ["$filter", function ($filter) {       
    return function(amount, currencySymbol){
        var currency = $filter('currency');         

        if(amount < 0){
           return currency(amount, currencySymbol).replace("-", "(") + ')'
        }

        return currency(amount, currencySymbol);
    };
}]);