Microservices Interview Questions and Answers

Docker helps in many ways for microservices architecture.

1. In a microservice architecture, there can be many different services written in different languages. So a developer might have to setup few services along with its dependency and platform requirements. This becomes difficult with the growing number of services in an ecosystem. However, this becomes very easy if these services run inside a Docker container.

2. Running services inside a container also give a similar setup across all the environments, i.e development, staging and production.

3. Docker also helps in scaling along with container orchestration.

4. Docker helps to upgrade the underlying language very easily. We can save many man-hours.

5. Docker helps to onboard the engineers fast.

6. Docker also helps to reduce the dependencies on IT Teams to set up and manage the different kind of environment required.

How would you manage application configuration in microservice running in a container?

As container based deployment involves a single image per microservice, it is a bad idea to bundle the configuration along with the image.

This approach is not at all scalable because we might have multiple environments and also we might have to take care of geographically distributed deployments where we might have different configurations as well.

Also, when there are application and cron application as part of the same codebase, it might need to take additional care on production as it might have repercussions how the crons are architected.

To solve this, we can put all our configuration in a centralized config service which can be queried by the application for all its configurations at the runtime. Spring cloud is one of the example services which provides this facility.

It also helps to secure the information, as the configuration might have passwords or access to reports or database access controls. Only trusted parties should be allowed to access these details for security reasons.

What is container orchestration and how does it helps in a microservice architecture?

In a production environment, you don’t just deal with the application code/application server. You need to deal with API Gateway, Proxy Servers, SSL terminators, Application Servers, Database Servers, Caching Services, and other dependent services.

As in modern microservice architecture where each microservice runs in a separate container, deploying and managing these containers is very challenging and might be error-prone.

Container orchestration solves this problem by managing the life cycle of a container and allows us to automate the container deployments.

It also helps in scaling the application where it can easily bring up a few containers. Whenever there is a high load on the application and once the load goes down. it can scale down as well by bringing down the containers. It is helpful to adjust cost based on requirements.

Also in some cases, it takes care of internal networking between services so that you need not make any extra effort to do so. It also helps us to replicate or deploy the docker images at runtime without worrying about the resources. If you need more resources, you can configure that in orchestration services and it will be available/deployed on production servers within minutes.

Data structures Interview Questions

Practice Problems

1. What is a data structure?

The data structure is the way data is organized (stored) and manipulated for retrieval and access. It also defines the way different sets of data relate to one another, establishing relationships and forming algorithms.

2. What is a linear data structure? Name a few examples.

A data structure is linear if all its elements or data items are arranged in a sequence or a linear order. The elements are stored in a non-hierarchical way so that each item has successors and predecessors except the first and last element in the list.

Examples of linear data structures are Arrays, Stack, Strings, Queue, and Linked List.

3. What are some applications of data structures? 

Numerical analysis, operating system, AI, compiler design, database management, graphics, statistical analysis, and simulation.

4. What is the difference between file structure and storage structure?

The difference lies in the memory area accessed. Storage structure refers to the data structure in the memory of the computer system, whereas file structure represents the storage structure in the auxiliary memory.

5. What is a linked list data structure?

It’s a linear data structure or a sequence of data objects where elements are not stored in adjacent memory locations. The elements are linked using pointers to form a chain. Each element is a separate object, called a node.  Each node has two items: a data field and a reference to the next node. The entry point in a linked list is called the head. Where the list is empty, the head is a null reference and the last node has a reference to null.

A linked list is a dynamic data structure, where the number of nodes is not fixed, and the list has the ability to grow and shrink on demand.

It is applied in cases where:

• We deal with an unknown number of objects or don’t know how many items are in the list
• We need constant-time insertions/deletions from the list, as in real-time computing where time predictability is critical
• Random access to any elements is not needed
• The algorithm requires a data structure where objects need to be stored irrespective of their physical address in memory
• We need to insert items in the middle of the list as in a priority queue

Some implementations are stacks and queues, graphs, directory of names, dynamic memory allocation, and performing arithmetic operations on long integers.

6. Are linked lists considered linear or non-linear data structures?

Linked lists are considered both linear and non-linear data structures depending upon the application they are used for. When used for access strategies, it is considered as a linear data-structure. When used for data storage, it is considered a non-linear data structure.

7. What are the advantages of a linked list over an array? In which scenarios do we use Linked List and when Array?

Advantages of a linked list over an array are:

1. Insertion and Deletion

Insertion and deletion of nodes is an easier process, as we only update the address present in the next pointer of a node. It’s expensive to do the same in an array as the room has to be created for the new elements and existing elements must be shifted.

2. Dynamic Data Structure

As a linked list is a dynamic data structure, there is no need to give an initial size as it can grow and shrink at runtime by allocating and deallocating memory. However, the size is limited in an array as the number of elements is statically stored in the main memory.

3. No wastage of memory

As the size of a linked list can increase or decrease depending on the demands of the program, and memory is allocated only when required, there is no memory wasted. In the case of an array, there is memory wastage. For instance, if we declare an array of size 10 and store only five elements in it, then the space for five elements is wasted.

4. Implementation

Data structures like stack and queues are more easily implemented using a linked list than an array.

Some scenarios where we use linked list over array are:

• When we know the upper limit on the number of elements in advance
• When there are a large number of add or remove operations
• When there are no large number of random access to elements
• When we want to insert items in the middle of the list, such as when implementing a priority queue

Some scenarios in which we use array over the linked list are:

• When we need to index or randomly access elements
• When we know the number of elements in the array beforehand, so we can allocate the correct amount of memory
• When we need speed when iterating through all the elements in the sequence
• When memory is a concern; filled arrays use less memory than linked lists, as each element in the array is the data but each linked list node requires the data as well as one or more pointers to the other elements in the linked list

In summary, we consider the requirements of space, time, and ease of implementation to decide whether to use a linked list or array.

8. What is a doubly-linked list? Give some examples.

It is a complex type (double-ended LL) of a linked list in which a node has two links, one that connects to the next node in the sequence and another that connects to the previous node. This allows traversal across the data elements in both directions. 

Examples include: 

• A music playlist with next and previous navigation buttons
• The browser cache with BACK-FORWARD visited pages
• The undo and redo functionality on a browser, where you can reverse the node to get to the previous page

9. How do you reference all of the elements in a one-dimension array?

All of the elements in a one-dimension array can be referenced using an indexed loop as the array subscript so that the counter runs from 0 to the array size minus one. 

10. What are dynamic data structures? Name a few.

They are collections of data in memory that expand and contract to grow or shrink in size as a program runs. This enables the programmer to control exactly how much memory is to be utilized.

Examples are the dynamic array, linked list, stack, queue, and heap.

An algorithm is a step by step method of solving a problem or manipulating data. It defines a set of instructions to be executed in a certain order to get the desired output. 

12. Why do we need to do an algorithm analysis?

A problem can be solved in more than one way using several solution algorithms. Algorithm analysis provides an estimation of the required resources of an algorithm to solve a specific computational problem. The amount of time and space resources required to execute is also determined.

The time complexity of an algorithm quantifies the amount of time taken for an algorithm to run as a function of the length of the input. The space complexity quantifies the amount of space or memory taken by an algorithm, to run as a function of the length of the input.

13. What is a stack?

A stack is an abstract data type that specifies a linear data structure, as in a real physical stack or piles where you can only take the top item off the stack in order to remove things. Thus, insertion (push) and deletion (pop) of items take place only at one end called top of the stack, with a particular order: LIFO (Last In First Out) or FILO (First In Last Out).

14. Where are stacks used?

• Expression, evaluation, or conversion of evaluating prefix, postfix, and infix expressions
• Syntax parsing
• String reversal
• Parenthesis checking
• Backtracking

15. What is a queue data structure? 

A queue is an abstract data type that specifies a linear data structure or an ordered list,  using the First In First Out (FIFO) operation to access elements. Insert operations can be performed only at one end called REAR and delete operations can be performed only at the other end called FRONT. 

16. List some applications of queue data structure.

To prioritize jobs as in the following scenarios:

• As waiting lists for a single shared resource in a printer, CPU, call center systems, or image uploads; where the first one entered is the first to be processed
• In the asynchronous transfer of data; or example pipes, file IO, and sockets
• As buffers in applications like MP3 media players and CD players
• To maintain the playlist in media players (to add or remove the songs)

17. What is a Dequeue?

It is a double-ended queue, or a data structure, where the elements can be inserted or deleted at both ends (FRONT and REAR).

18. What operations can be performed on queues?

• enqueue() adds an element to the end of the queue
• dequeue() removes an element from the front of the queue
• init() is used for initializing the queue
• isEmpty tests for whether or not the queue is empty
• The front is used to get the value of the first data item but does not remove it
• The rear is used to get the last item from a queue

19. What are the advantages of the heap over a stack?

Generally, both heap and stack are part of memory and used in Java for different needs: 

• Heap is more flexible than the stack because memory space can be dynamically allocated and de-allocated as needed 
• Heap memory is used to store objects in Java, whereas stack memory is used to store local variables and function call 
• Objects created in the heap are visible to all threads, whereas variables stored in stacks are only visible to the owner as private memory
• When using recursion, the size of heap memory is more whereas it quickly fill-ups stack memory 

20. Where can stack data structure be used?

• Expression evaluation
• Backtracking
• Memory management
• Function calling and return

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Advanced Angular Interview Questions

 

 1. In Angular, describe how will you set, get and clear cookies?

For using cookies in Angular, you need to include a  module called ngCookies angular-cookies.js.

To set Cookies – For setting the cookies in a key-value format ‘put’ method is used.

cookie.set('nameOfCookie',"cookieValue");

To get Cookies – For retrieving the cookies ‘get’ method is used.

cookie.get(‘nameOfCookie’);

To clear Cookies – For removing cookies ‘remove’ method is used.

cookie.delete(‘nameOfCookie’);

2.  If your data model is updated outside the ‘Zone’, explain the process how will you the view?

You can update your view using any of the following:

1. ApplicationRef.prototype.tick(): It will perform change detection on the complete component tree.
2. NgZone.prototype.run(): It will perform the change detection on the entire component tree. Here, the run() under the hood will call the tick itself and then parameter will take the function before tick and executes it.
3. ChangeDetectorRef.prototype.detectChanges(): It will launch the change detection on the current component and its children.

3. Explain ng-app directive in Angular.

ng-app directive is used to define Angular applications which let us use the auto-bootstrap in an Angular application. It represents the root element of an Angular application and is generally declared near <html> or <body> tag. Any number of ng-app directives can be defined within an HTML document but just a single Angular application can be officially bootstrapped implicitly. Rest of the applications must be manually bootstrapped.

Example

<div ng-app=“myApp” ng-controller=“myCtrl”>
First Name :
<input type=“text” ng-model=“firstName”>
<br />
Last Name :
<input type=“text” ng-model=“lastName”>
<br>
Full Name: {{firstName + ” ” + lastName }}
</div>  

4. What is the process of inserting an embedded view from a prepared TemplateRef?

@Component({
    selector: 'app-root',
    template: `
        <ng-template #template let-name='fromContext'><div>{{name}}</ng-template>
    `
})
export class AppComponent implements AfterViewChecked {
    @ViewChild('template', { read: TemplateRef }) _template: TemplateRef<any>;
    constructor() { }

    ngAfterViewChecked() {
        this.vc.createEmbeddedView(this._template, {fromContext: 'John'});
    }
}

5. How can you hide an HTML element just by a button click in angular?

An HTML element can be easily hidden using the ng-hide directive in conjunction along with a controller to hide an HTML element on button click.

View

<div ng-controller="MyController">
  <button ng-click="hide()">Hide element</button>
  <p ng-hide="isHide">Hello World!</p>
</div>

Controller

controller: function() {
this.isHide = false;
this.hide = function(){
this.isHide = true; }; }

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Angular Interview Questions and Answers

Please click this link for set of angular questions

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1. Differentiate between Angular and AngularJS.

Feature	AngularJS	Angular
Architecture	Supports MVC design model	Uses components and directives
Language	Recommended Language: JavaScript	Recommended Language: TypeScript
Expression Syntax	Specific ng directive is required for the image/property and an event	Uses () to bind an event and [] for property binding
Mobile Support	Doesn’t provide any mobile support	Provides mobile support
Routing	$routeprovider.when() is used for routing configs	@RouteConfig{(…)} is used for routing config
Dependency Injection	Doesn’t supports the concept of Dependency Injection	Supports hierarchical Dependency Injection with a unidirectional tree-based change detection
Structure	Less manageable	Simplified structure and makes the development and maintenance of large applications easier
Speed	With two-way data binding development effort and time are reduced	Faster than AngularJS with upgraded features
Support	No support or new updates are provided anymore	Active support and frequent new updates are made

3. What are the advantages of using Angular?

A few of the major advantages of using Angular framework are listed below:

• It supports two-way data-binding
• It follows MVC pattern architecture
• It supports static template and Angular template
• You can add a custom directive
• It also supports RESTfull services
• Validations are supported
• Client and server communication is facilitated
• Support for dependency injection
• Has strong features like Event Handlers, Animation, etc.

5. What are Angular expressions?

Angular expressions are code snippets that are usually placed in binding such as {{ expression }} similar to JavaScript. These expressions are used to bind application data to HTML

Syntax: {{ expression }}

6. What are templates in Angular?

Templates in Angular are written with HTML that contains Angular-specific elements and attributes. These templates are combined with information coming from the model and controller which are further rendered to provide the dynamic view to the user.

7. In Angular what is string interpolation?

String interpolation in Angular is a special syntax that uses template expressions within double curly {{ }} braces for displaying the component data. It is also known as moustache syntax. The JavaScript expressions are included within the curly braces to be executed by Angular and the relative output is then embedded into the HTML code. These expressions are usually updated and registered like watches, as a part of the digest cycle.

8. What is the difference between an Annotation and a Decorator in Angular?

Annotations in angular are “only” metadata set of the class using the Reflect Metadata library. They are used to create an “annotation” array. On the other hand, decorators are the design patterns that are used for separating decoration or modification of a class without actually altering the original source code.

9. What do you understand by controllers in Angular?

Controllers are JavaScript functions which provide data and logic to HTML UI. As the name suggests, they control how data flows from the server to HTML UI.

10. What is scope in Angular?

Scope in Angular is an object that refers to the application model. It is an execution context for expressions. Scopes are arranged in a hierarchical structure which mimics the DOM structure of the application. Scopes can watch expressions and propagate events.

11. What are directives in Angular?

A core feature of Angular, directives are attributes that allow you to write new HTML syntax, specific to your application. They are essentially functions that execute when the Angular compiler finds them in the DOM.  The Angular directives are segregated into 3 parts:

1. Component Directives
2. Structural Directives
3. Attribute Directives

12. What is data binding?

In Angular, data binding is one of the most powerful and important features that allow you to define the communication between the component and DOM(Document Object Model). It basically simplifies the process of defining interactive applications without having to worry about pushing and pulling data between your view or template and component. In Angular, there are four forms of data binding:

1.  String Interpolation
2. Property Binding
3. Event Binding
4. Two-Way Data Binding

13. What is the purpose of a filter in Angular?

Filters in Angular are used for formatting the value of an expression in order to display it to the user. These filters can be added to the templates, directives, controllers or services. Not just this, you can create your own custom filters. Using them, you can easily organize data in such a way that the data is displayed only if it fulfills certain criteria. Filters are added to the expressions by using the pipe character |, followed by a filter.

14. What are the differences between Angular and jQuery?

Features	jQuery	Angular
DOM Manipulation	Yes	Yes
RESTful API	No	Yes
Animation Support	Yes	Yes
Deep Linking Routing	No	Yes
Form Validation	No	Yes
Two Way Data Binding	No	Yes
AJAX/JSONP	Yes	Yes

15. What is a provider in Angular?

A provider is a configurable service in Angular. It is an instruction to the Dependency Injection system that provides information about the way to obtain a value for a dependency. It is an object that has a $get() method which is called to create a new instance of a service. A Provider can also contain additional methods and uses $provide in order to register new providers.

16. Does Angular support nested controllers?

Yes, Angular does support the concept of nested controllers. The nested controllers are needed to be defined in a hierarchical manner for using it in the View. 

17. How can you differentiate between Angular expressions and JavaScript expressions?

Angular Expressions	JavaScript Expressions
1. They can contain literals, operators, and variables.	1. They can contain literals, operators, and variables.
2. They can be written inside the HTML tags.	2. They can’t be written inside the HTML tags.
3. They do not support conditionals, loops, and exceptions.	3. They do support conditionals, loops, and exceptions.
4.  They support filters.	4.  They do not support filters.

18. List at down the ways in which you can communicate between applications modules using core Angular functionality.

Below are the most general ways for communicating between application modules using core Angular functionality :

• Using events
• Using services
• By assigning models on $rootScope
• Directly between controllers [$parent, $$childHead, $$nextSibling, etc.]
• Directly between controllers [ControllerAs, or other forms of inheritance]

19. What is the difference between a service() and a factory()?

A service() in Angular is a function that is used for the business layer of the application. It operates as a constructor function and is invoked once at the runtime using the ‘new’ keyword. Whereas factory() is a function which works similar to the service() but is much more powerful and flexible. factory() are design patterns which help in creating Objects.

20. What is the difference between $scope and scope in Angular?

• $scope in Angular is used for implementing the concept of dependency injection (D.I) on the other hand scope is used for directive linking.
• $scope is the service provided by $scopeProviderwhich can be injected into controllers, directives or other services whereas Scope can be anything such as a function parameter name, etc.

21. Explain the concept of scope hierarchy?

The $scope objects in Angular are organized into a hierarchy and are majorly used by views. It contains a root scope which can further contain scopes known as child scopes. One root scope can contain more than one child scopes. Here each view has its own $scope thus the variables set by its view controller will remain hidden to the other controllers. The Scope hierarchy generally looks like:

• Root $scope
  • $scope for Controller 1
  • $scope for Controller 2
  • ..
  • $scope for Controller ‘n’

22. What is AOT?

AOT stands for Angular Ahead-of-Time compiler. It is used for pre-compiling the application components and along with their templates during the build process. Angular applications which are compiled with AOT has a smaller launching time. Also, components of these applications can execute immediately, without needing any client-side compilation. Templates in these applications are embedded as code within their components. It reduces the need for downloading the Angular compiler which saves you from a cumbersome task. AOT compiler can discard the unused directives which are further thrown out using a tree-shaking tool.

23. Explain jQLite.

jQlite is also known as jQuery lite is a subset of jQuery and contains all its features. It is packaged within Angular, by default. It helps Angular to manipulate the DOM in a way that is compatible cross-browser. jQLite basically implements only the most commonly needed functionality which results in having a small footprint.

24. Explain the process of digest cycle in Angular?

The digest cycle in Angular is a process of monitoring the watchlist for keeping a track of changes in the value of the watch variable. In each digest cycle, Angular compares the previous and the new version of the scope model values. Generally, this process is triggered implicitly but you can activate it manually as well by using $apply().

25. What are the Angular Modules?

All the Angular apps are modular and follow a modularity system known as NgModules. These are the containers which hold a cohesive block of code dedicated specifically to an application domain, a workflow, or some closely related set of capabilities. These modules generally contain components, service providers, and other code files whose scope is defined by the containing NgModule.  With modules makes the code becomes more maintainable, testable, and readable. Also, all the dependencies of your applications are generally defined in modules only.

26. On which types of the component can we create a custom directive?

Angular provides support to create custom directives for the following:

• Element directives − Directive activates when a matching element is encountered.
• Attribute − Directive activates when a matching attribute is encountered.
• CSS − Directive activates when a matching CSS style is encountered.
• Comment − Directive activates when a matching comment is encountered

27. What are the different types of filters in Angular?

Below are the various filters supported by Angular:

• currency: Format a number to a currency format.
• date: Format a date to a specified format.
• filter: Select a subset of items from an array.
• json: Format an object to a JSON string.
• limit: To Limits an array/string, into a specified number of elements/characters.
• lowercase: Format a string to lower case.
• number: Format a number to a string.
• orderBy: Orders an array by an expression.
• uppercase: Format a string to upper case.

28. What is Dependency Injection in Angular? 

Dependency Injection (DI) is a software design pattern where the objects are passed as dependencies rather than hard-coding them within the component. The concept of Dependency Injection comes in handy when you are trying to separate the logic of object creation to that of its consumption. The ‘config’ operation makes use of DI that must be configured beforehand while the module gets loaded to retrieve the elements of the application. With this feature, a user can change dependencies as per his requirements.

29. Differentiate between one-way binding and two-way data binding.

In One-Way data binding, the View or the UI part does not update automatically whenever the data model changes. You need to manually write custom code in order to update it every time the view changes.

Whereas, in Two-way data binding, the View or the UI part is updated implicitly as soon as the data model changes. It is a synchronization process, unlike One-way data binding.

30. What are the lifecycle hooks for components and directives?

An Angular component has a discrete life-cycle which contains different phases as it transits through birth till death. In order to gain better control of these phases, we can hook into them using the following:

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• constructor: It is invoked when a component or directive is created by calling new on the class.
• ngOnChanges: It is invoked whenever there is a change or update in any of the input properties of the component.
• ngOnInit: It is invoked every time a given component is initialized. This hook is only once called in its lifetime after the first ngOnChanges.
• ngDoCheck: It is invoked whenever the change detector of the given component is called. This allows you to implement your own change detection algorithm for the provided component.
• ngOnDestroy: It is invoked right before the component is destroyed by Angular. You can use this hook in order to unsubscribe observables and detach event handlers for avoiding any kind of memory leaks.

31. What do you understand by dirty checking in Angular?

In Angular, the digest process is known as dirty checking. It is called so as it scans the entire scope for changes. In other words, it compares all the new scope model values with the previous scope values. Since all the watched variables are contained in a single loop, any change/update in any of the variable leads to reassigning of rest of the watched variables present inside the DOM. A watched variable is in a single loop(digest cycle), any value change of any variable forces to reassign values of other watched variables in DOM

32. Differentiate between DOM and BOM.

DOM	BOM
1. Stands for Document Object Model	1. Stands for Browser Object Model
2. Represents the contents of a web page	2. Works a level above web page and includes browser attributes
3. All the Objects are arranged in a tree structure and the document can be manipulated & accessed via provided APIs only	3. All global JavaScript objects, variables & functions become members of the window object implicitly
4. Manipulates HTML documents	4. Access and manipulate the browser window
5. W3C Recommended standard specifications	5. Each browser has its own implementation

33. What is Transpiling in Angular?
Transpiling in Angular refers to the process of conversion of the source code from one programming language to another. In Angular, generally, this conversion is done from TypeScript to JavaScript. It is an implicit process and happens internally.

34. How to perform animation in Angular?

In order to perform animation in an Angular application, you need to include a special Angular library known as Animate Library and then refer to the ngAnimate module into your application or add the ngAnimate as a dependency inside your application module.

35. What is transclusion in Angular?

The transclusion in Angular allows you to shift the original children of a directive into a specific location within a new template. The ng directive indicates the insertion point for a transcluded DOM of the nearest parent directive that is using transclusion. Attribute directives like ng-transclude or ng-transclude-slot are mainly used for transclusion.

36. What are events in Angular?

Events in Angular are specific directives that help in customizing the behavior of various DOM events. Few of the events supported by Angular are listed below:

• ng-click
• ng-copy
• ng-cut
• ng-dblclick
• ng-keydown
• ng-keypress
• ng-keyup
• ng-mousedown
• ng-mouseenter
• ng-mouseleave
• ng-mousemove
• ng-mouseover
• ng-mouseup
• ng-blur

37. List some tools for testing angular applications?

1. Karma
2. Angular Mocks
3. Mocha
4. Browserify
5. Sion

38. How to create a service in Angular?

In Angular, a service is a substitutable object that is wired together using dependency injection. A service is created by registering it in the module it is going to be executed within. There are basically three ways in which you can create an angular service. They are basically three ways in which a service can be created in Angular:

• Factory
• Service
• Provider

39. What is a singleton pattern and where we can find it in Angular?

Singleton pattern in Angular is a great pattern which restricts a class from being used more than once. Singleton pattern in Angular is majorly implemented on dependency injection and in the services. Thus, if you use ‘new Object()’ without making it a singleton, then two different memory locations will be allocated for the same object. Whereas, if the object is declared as a singleton, in case it already exists in the memory then simply it will be reused.

40. What do you understand by REST in Angular?

REST stands for REpresentational State Transfer. REST is an API (Application Programming Interface) style that works on the HTTP request. In this, the requested URL pinpoints the data that needs to be processed. Further ahead, an HTTP method then identifies the specific operation that needs to be performed on that requested data. Thus, the APIs which follows this approach are known as RESTful APIs.

41. What is bootstrapping in Angular?

Bootstrapping in Angular is nothing but initializing, or starting the Angular app. Angular supports automatic and manual bootstrapping.

• Automatic Bootstrapping: this is done by adding the ng-app directive to the root of the application, typically on the tag or tag if you want angular to bootstrap your application automatically. When Angular finds ng-app directive, it loads the module associated with it and then compiles the DOM.
• Manual Bootstrapping: Manual bootstrapping provides you more control on how and when to initialize your Angular application. It is useful where you want to perform any other operation before Angular wakes up and compile the page.

42. What is the difference between a link and compile in Angular?

• Compile function is used for template DOM Manipulation and to collect all the directives.
• Link function is used for registering DOM listeners as well as instance DOM manipulation and is executed once the template has been cloned.

43. What do you understand by constants in Angular?

In Angular, constants are similar to the services which are used to define the global data. Constants are declared using the keyword “constant”. They are created using constant dependency and can be injected anywhere in controller or services.

44. What is the difference between a provider, a service and a factory in Angular?

Provider	Service	Factory
A provider is a method using which you can pass a portion of your application into app.config	A service is a method that is used to create a service instantiated with the ‘new’ keyword.	It is a method that is used for creating and configuring services. Here you create an object, add properties to it and then return the same object and pass the factory method into your controller.

45. What are Angular Global APIs?

Angular Global API is a combination of global JavaScript functions for performing various common tasks like:

• Comparing objects
• Iterating objects
• Converting data

There are some common Angular Global API functions like:

• angular. lowercase: Converts a string to lowercase string.
• angular. uppercase: Converts a string to uppercase string.
• angular. isString: Returns true if the current reference is a string.
• angular. isNumber: Returns true if the current reference is a number.
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