Interview questions angular and node

 1)Template ref vs element ref in angular:

In a simplified way, the main difference between ElementRef and TemplateRef in Angular is as follows:

ElementRef:

Represents a reference to a specific element in the DOM (Document Object Model).

Provides access to the native element, allowing you to manipulate its properties and invoke native DOM methods.

It's useful when you need direct access to the underlying HTML element for tasks such as changing styles, manipulating attributes, or performing other DOM-related operations.

TemplateRef:

Represents a reference to an Angular template, which is a section of markup that can be instantiated.

It doesn't provide direct access to the native element, but rather represents a reusable piece of UI structure that can be dynamically rendered in different parts of your application.

It's useful when you want to define a template once and reuse it in multiple places, such as using ngTemplateOutlet or creating dynamic components with ViewContainerRef.

In summary, ElementRef gives you direct access to the underlying DOM element, while TemplateRef represents a reusable Angular template that can be dynamically rendered. ElementRef is more suitable for DOM manipulation, while TemplateRef is used for creating dynamic and reusable templates.

3)auth guard ,can activate,

1. CanActivate:

   • The CanActivate guard is used to determine if a user is allowed to activate (navigate to) a specific route.
   • It checks if the user meets certain criteria, such as being authenticated or having specific roles or permissions.
   • Example: AuthGuard implements CanActivate

2. CanActivateChild:

   • The CanActivateChild guard is similar to CanActivate but specifically for child routes.
   • It is used to protect child routes within a parent route and controls access to child routes based on the same criteria as CanActivate.
   • Example: AuthGuard implements CanActivateChild

3. CanLoad:

   • The CanLoad guard is used to control whether a module or lazy-loaded feature module can be loaded.
   • It is primarily used for feature modules loaded lazily to ensure that the module is only loaded if the user has the necessary permissions.
   • Example: AuthGuard implements CanLoad

4. CanDeactivate:

   • The CanDeactivate guard is used to control whether a user is allowed to deactivate (leave) a specific route or component.
   • It checks if the user can safely leave the current route/component, such as when there are unsaved changes or a confirmation is required.
   • Example: CanDeactivateGuard implements CanDeactivate<Component>

5. Resolve:

   • The Resolve guard is used to fetch some data before activating a route.
   • It helps resolve asynchronous data dependencies and ensures that the route is activated only when the data is available.
   • Example: ResolveGuard implements Resolve<Data>
   


4)error handler and global error handler?

Both the error handler middleware and the global error handler serve different purposes. The error handler middleware is focused on handling errors that occur during the request processing flow, allowing you to customize the error response for the specific request. On the other hand, the global error handler is used to catch unhandled exceptions or rejections that may occur outside the regular request flow, providing a centralized mechanism to handle such errors.

To implement a global error handler in Node.js, you can attach event listeners to the uncaughtException and unhandledRejection events of the process object. Here's an example of how you can set up a global error handler in Node.js:

process.on('uncaughtException', function(err) { // Custom error handling logic console.error('Uncaught Exception:', err); process.exit(1); }); process.on('unhandledRejection', function(reason, promise) { // Custom error handling logic console.error('Unhandled Rejection:', reason); process.exit(1); });

5)pagniation in MongoDB?

_inventoryItems

            .aggregate(

                [

                    { $match: queryfilters },

                    {

                        '$facet': {

                            metadata: [{ $count: "total" }],

                            data: [

                                { $sort: sortOrder },

                                { $skip: parseInt(_page.size) * parseInt(_page.pageNumber - 1) },

                                { $limit: parseInt(_page.size) },

                            ]

                        }

                    }

                ]).toArray();

In MongoDB, the $facet operator allows you to run multiple aggregation pipelines within a single query request. It enables you to perform multiple independent aggregations on the same set of documents and return the results as an array of sub-results.

7)partial key MongoDB?

8)scrum and kanban?

Scrum is a specific framework within Agile that provides a structured approach with sprints and defined roles. Kanban, on the other hand, is an Agile methodology focused on visualizing and optimizing workflow using a visual board and limiting work in progress.

It's important to note that these are simplified explanations, and each methodology has more depth and specific practices that can be tailored to different contexts and projects.

9)backpressure in streaming?

Backpressure in streaming refers to a mechanism that allows a receiver to control the rate at which data is sent by the sender. It helps to ensure that the receiver can handle the data being sent without getting overwhelmed or running out of memory.

To explain backpressure in Node.js streaming in an easy way, let's consider a real-life scenario:

Imagine you have a faucet that is pouring water into a cup. The faucet represents the data source (sender), and the cup represents the data destination (receiver).

In a scenario without backpressure, the faucet pours water at its own full speed, and the cup has to handle whatever amount of water comes its way. If the cup is not big enough or cannot handle the water fast enough, it might overflow or cause a mess.

Now, let's introduce backpressure into the scenario:

With backpressure, the cup communicates its capacity to the faucet. As the cup gets filled, it signals the faucet to slow down or stop pouring water until it is ready to handle more. This way, the cup controls the flow of water, ensuring that it never overflows.

Similarly, in Node.js streaming, backpressure allows the receiver (e.g., a readable stream) to control the flow of data from the sender (e.g., a writable stream). If the receiver cannot handle the incoming data as fast as it arrives, it can pause or signal the sender to slow down until it is ready to receive more data.

This backpressure mechanism is built into Node.js streams, allowing efficient handling of large amounts of data without overwhelming the system's memory or causing data loss.

In summary, backpressure in Node.js streaming is like the cup controlling the flow of water from a faucet. It ensures that the receiver can handle the data at its own pace, preventing memory issues and allowing for smooth and efficient data transfer.

10)updateone upsert ?

In MongoDB, the updateOne() method with the upsert option allows you to update a document if it exists or insert a new document if it doesn't exist. The upsert option combines the functionality of both updating and inserting in a single operation.

The { upsert: true } option is passed as the third argument to updateOne(), enabling the upsert functionality.

11)Dependency injection in angular?

Dependency injection in Angular is a mechanism that allows you to provide and use the required dependencies of a component or service without explicitly creating them within the component or service. It simplifies the management of dependencies by letting Angular take care of creating and providing them for you.

In simpler terms, think of dependency injection as a way to get the things you need (dependencies) without having to worry about where they come from. Angular will automatically provide those dependencies for you based on the configuration you set up.

For example, let's say you have a component that needs to fetch data from an API. Instead of manually creating an HTTP client within the component, you can declare the HTTP client as a dependency in the component's constructor. Angular's dependency injection system will then take care of creating and providing an instance of the HTTP client when the component is created, allowing you to use it seamlessly.

By using dependency injection, you can easily manage and test your code, as dependencies can be easily swapped or mocked for testing purposes. It also promotes modular and reusable code since components and services can be developed independently and easily plugged into other parts of your application.

12)Abort controller to cancel API :

In JavaScript, you can cancel an API request using the AbortController and AbortSignal objects. These objects are part of the browser's built-in Fetch API and can be used to control and abort asynchronous operations such as API requests.

Here's an example of how to cancel an API request in JavaScript:

1. Create an instance of the AbortController:

javascript
const controller = new AbortController();

2. Get the AbortSignal from the AbortController:

javascript
const signal = controller.signal;

3. Make the API request using the Fetch API and pass the signal in the request options:

javascript
fetch('https://api.example.com/data', { signal })
  .then(response => response.json())
  .then(data => {
    // Process the API response
  })
  .catch(error => {
    if (error.name === 'AbortError') {
      // Request was aborted
    } else {
      // Handle other errors
    }
  });

4. To cancel the API request, call the abort() method on the AbortController:

javascript
controller.abort();

When the abort() method is called, the API request associated with the AbortSignal will be canceled. The promise returned by the fetch call will reject with an "AbortError" and can be caught in the catch block for handling.

It's important to note that not all APIs support cancellation. The server must support the AbortController and handle the cancellation appropriately. If the API request is made using other libraries or frameworks, they may provide their own mechanisms for canceling requests.

13)loader in angular:

<div *ngIf="isLoading">
  <mat-spinner></mat-spinner> <!-- Replace with your desired spinner component -->
</div>

makeAPICall(): void {
  this.isLoading = true;

  this.http.get('https://api.example.com/data')
    .pipe(finalize(() => this.isLoading = false))
    .subscribe(response => {
      // Process the API response
    }, error => {
      // Handle API call errors
    });
}

1. The makeAPICall() method is defined as a void function without any arguments.

2. Within the function, this.isLoading is set to true to indicate that an API call is in progress and the spinner should be displayed.

3. The this.http.get() method is used to make an HTTP GET request to the specified URL ('https://api.example.com/data').

4. The pipe() function allows you to apply operators to the observable stream. In this case, the finalize() operator is used.

5. The finalize() operator is used to define a callback function that will be executed when the observable completes or errors out, regardless of the outcome. In this case, the callback function sets this.isLoading back to false to indicate that the API call has finished.

6. The subscribe() function is called on the observable returned by the http.get() method. It takes two callback functions as arguments: one to handle the API response and another to handle any errors.

7. In the success callback (response => { /* Process the API response */ }), you can write the logic to handle the API response, such as updating component variables or rendering the data on the UI.

8. In the error callback (error => { /* Handle API call errors */ }), you can define how to handle errors that may occur during the API call, such as displaying an error message or taking appropriate actions.

By setting isLoading to true before making the API call and using the finalize() operator to set it back to false when the API call is completed (successfully or with an error), the isLoading variable serves as a flag to control the visibility of the spinner in your HTML template.

You can call the makeAPICall() method from your component or template to initiate the API request and see the spinner in action while the call is in progress. 

14)New in js apart from es6,WebGL,geolocation, storage,webgl?

1. ECMAScript 2019 (ES10): ES10 introduced features like Array.prototype.flat() and Array.prototype.flatMap() for working with nested arrays, optional catch binding, Object.fromEntries() for transforming key-value arrays into objects, and the Symbol.prototype.description property for accessing the description of a Symbol.

2. 
   

3. ECMAScript 2021 (ES12): Some features introduced in ES12 include the String.prototype.replaceAll() method for global string replacement, the Logical Assignment Operators (e.g., ||=, &&=) for concise assignment with logical operators, and the Numeric Separators for improved readability of large numeric literals.

4. 
   
5. Optional Chaining Operator (?.) for more concise and safer code.

const object1 = {

  a: 'somestring',

  b: 42

};

for (const [key, value] of Object.entries(object1)) {

  console.log(`${key}: ${value}`);

}