Why is the variable name “$scope” necessary ?

Question

I\'m fairly new to Javascript ( just finished the book Eloquent Javascript ), and am currently reading AngularJS from O\'Reilly. And getting this small snippet of code to w

Answer 1

Because the Angular uses the name of the parameter in its dependency injection system, which constructs the controller.

Answer 2

Both previous answers are correct , just you should know that you can "override" the default behavior if you're declaring a controller this way:

module.controller("ControllerName",["$scope",function( custom_name ){ ... }]);

Example:

var app = angular.module("myApp",[]);

app.controller("TextController",["$scope",function(glue){
    glue.name1 = "John";
    glue.name2 = "Paul";
    glue.name3 = "George";
    glue.name4 = "Ringo";
}]);

and then:

<div ng-controller="TextController">
    Hello {{ name1 }}, {{ name2 }}, {{ name3 }}, {{ name4 }}!
</div>

Working here: http://jsfiddle.net/d4M2P/

Answer 3

This is handled by the Angular injector.

http://docs.angularjs.org/api/auto/service/$injector

In JavaScript calling toString() on a function returns the function definition. The definition can then be parsed and the function arguments can be extracted. NOTE: This does not work with minification, and obfuscation tools since these tools change the argument names.

http://docs.angularjs.org/guide/di

Given a function the injector can infer the names of the service to inject by examining the function declaration and extracting the parameter names. In the above example $scope, and greeter are two services which need to be injected into the function.