directive.js

angular.module('gettext').directive('translate', function (gettextCatalog, $parse, $animate, $compile) {
    // Trim polyfill for old browsers (instead of jQuery)
    // Based on AngularJS-v1.2.2 (angular.js#620)
    var trim = (function () {
        if (!String.prototype.trim) {
            return function (value) {
                return (typeof value === 'string') ? value.replace(/^\s*/, '').replace(/\s*$/, '') : value;
            };
        }
        return function (value) {
            return (typeof value === 'string') ? value.trim() : value;
        };
    })();

    function assert(condition, missing, found) {
        if (!condition) {
            throw new Error('You should add a ' + missing + ' attribute whenever you add a ' + found + ' attribute.');
        }
    }

    return {
        restrict: 'A',
        terminal: true,
        compile: function compile(element, attrs) {
            // Validate attributes
            assert(!attrs.translatePlural || attrs.translateN, 'translate-n', 'translate-plural');
            assert(!attrs.translateN || attrs.translatePlural, 'translate-plural', 'translate-n');

            var html = trim(element.html());
            var translatePlural = attrs.translatePlural;

            return {
                post: function (scope, element, attrs) {
                    var countFn = $parse(attrs.translateN);
                    var pluralScope = null;
                    var msgidExp = attrs.translate ? $parse(attrs.translate) : function () { return html; };

                    function update() {
                        var msgid = msgidExp(scope);
                        if (!msgid) {
                            // wait until msgid is initialized
                            return;
                        }

                        // Fetch correct translated string.
                        var translated;
                        if (translatePlural) {
                            scope = pluralScope || (pluralScope = scope.$new());
                            scope.$count = countFn(scope);
                            translated = gettextCatalog.getPlural(scope.$count, msgid, translatePlural);
                        } else {
                            translated = gettextCatalog.getString(msgid);
                        }

                        // Swap in the translation
                        var newWrapper = angular.element('<span>' + translated + '</span>');
                        $compile(newWrapper.contents())(scope);
                        var oldContents = element.contents();
                        var newContents = newWrapper.contents();
                        $animate.enter(newContents, element);
                        $animate.leave(oldContents);
                    }

                    if (attrs.translateN) {
                        scope.$watch(attrs.translateN, update);
                    }

                    if (attrs.translate) {
                        scope.$watch(attrs.translate, update);
                    }

                    scope.$on('gettextLanguageChanged', update);

                    update();
                }
            };
        }
    };
});