prefill `input[type=url]` field with "http://" upon focus using an angular directive

prefill-url.js

// Prefill URL field with 'http://' upon focus.

<label class="item item-input" ng-if="vm.website === undefined || !vm.api && !vm.account">
  <input id="website" name="website" type="url" placeholder="What is your choir/chorus website?"
  ng-model="vm.website" required http-prefix>

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

app.directive('httpPrefix', function() {
    return {
        restrict: 'A',
        require: 'ngModel',
        link: function(scope, element, attrs, controller) {
            function ensureHttpPrefix(value) {
                // Need to add prefix if we don't have http:// prefix already AND we don't have part of it
                if(value && !/^(https?):\/\//i.test(value)
                   && 'http://'.indexOf(value) !== 0 && 'https://'.indexOf(value) !== 0 ) {
                    controller.$setViewValue('http://' + value);
                    controller.$render();
                    return 'http://' + value;
                }
                else
                    return value;
            }
            controller.$formatters.push(ensureHttpPrefix);
            controller.$parsers.splice(0, 0, ensureHttpPrefix);
        }
    };
});