foreach loop in angularjs

Questions 1 & 2

So basically, first parameter is the object to iterate on. It can be an array or an object. If it is an object like this :

var values = {name: 'misko', gender: 'male'};

Angular will take each value one by one the first one is name, the second is gender.

If your object to iterate on is an array (also possible), like this :

[{ "Name" : "Thomas", "Password" : "thomasTheKing" },
 { "Name" : "Linda", "Password" : "lindatheQueen" }]

Angular.forEach will take one by one starting by the first object, then the second object.

For each of this object, it will so take them one by one and execute a specific code for each value. This code is called the iterator function. forEach is smart and behave differently if you are using an array of a collection. Here is some exemple :

var obj = {name: 'misko', gender: 'male'};
var log = [];
angular.forEach(obj, function(value, key) {
  console.log(key + ': ' + value);
});
// it will log two iteration like this
// name: misko
// gender: male

So key is the string value of your key and value is ... the value. You can use the key to access your value like this : obj['name'] = 'John'

If this time you display an array, like this :

var values = [{ "Name" : "Thomas", "Password" : "thomasTheKing" },
           { "Name" : "Linda", "Password" : "lindatheQueen" }];
angular.forEach(values, function(value, key){
     console.log(key + ': ' + value);
});
// it will log two iteration like this
// 0: [object Object]
// 1: [object Object]

So then value is your object (collection), and key is the index of your array since :

[{ "Name" : "Thomas", "Password" : "thomasTheKing" },
 { "Name" : "Linda", "Password" : "lindatheQueen" }]
// is equal to
{0: { "Name" : "Thomas", "Password" : "thomasTheKing" },
 1: { "Name" : "Linda", "Password" : "lindatheQueen" }}

I hope it answer your question. Here is a JSFiddle to run some code and test if you want : http://jsfiddle.net/ygahqdge/

Debugging your code

The problem seems to come from the fact $http.get() is an asynchronous request.

You send a query on your son, THEN when you browser end downloading it it execute success. BUT just after sending your request your perform a loop using angular.forEach without waiting the answer of your JSON.

You need to include the loop in the success function

var app = angular.module('testModule', [])
    .controller('testController', ['$scope', '$http', function($scope, $http){
    $http.get('Data/info.json').then(function(data){
         $scope.data = data;

         angular.forEach($scope.data, function(value, key){
         if(value.Password == "thomasTheKing")
           console.log("username is thomas");
         });
    });

});

This should work.

Going more deeply

The $http API is based on the deferred/promise APIs exposed by the $q service. While for simple usage patterns this doesn't matter much, for advanced usage it is important to familiarize yourself with these APIs and the guarantees they provide.

You can give a look at deferred/promise APIs, it is an important concept of Angular to make smooth asynchronous actions.