What is the benefit of AngularJS Strict DI mode?

Question

Recently I come across with AngularJS Strict DI mode. What is the purpose & benefit of using it? Will we gain significant performance improvement by using it especially on mobile devices?

I try to apply it to my code and I did not do any annotation when writing the code. However, I have my code to be minify, and ng-annotate during build. But why is that after I add Strict DI mode to my code I still get the error saying "Explicit annotation required"?

Answer 1

Strict DI Mode basically throws errors when, at run time, it is found a piece of code that is not compliant to minification; but note that the code may be right and without logical-syntactical errors.

Citing the documentation:

if this attribute is present on the app element, the injector will be created in "strict-di" mode. This means that the application will fail to invoke functions which do not use explicit function annotation (and are thus unsuitable for minification), as described in the Dependency Injection guide, and useful debugging info will assist in tracking down the root of these bugs.

For example this code triggers an error because ($scope, $http, $filter) are not explicitly injected using $inject or giving to the .controller(A,B) method an array as second field.

angular.module("myApp", []) // BadController cannot be invoked, because // the dependencies to be injected are not // explicitly listed. .controller("BadController", function($scope, $http, $filter) {   // ... }); 

Right snippet:

angular.module("myApp", [])   .controller("GoodController1", GoodController1);  GoodController1.$inject = ["$scope", "$http", "$filter"];  function GoodController1($scope, $http, $filter){} 

or:

angular.module("myApp", [])   .controller("GoodController1",                ["$scope", "$http", "$filter", function ($scope, $http, $filter){      //... }]); 

In order to answer at your question there is no significant performance improvement by using it. It only grant to you the minifiability error safeness. This because minification changes variables names breaking your code when for example you use $scope without explicit annotation.