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What is the role of $http service in Angular.js?
The $http service is one of the core services in AngularJS that allows you to make HTTP requests to external resources such as RESTful APIs, web services, or backend servers. It provides a set of methods for performing common HTTP methods such as GET, POST, PUT, DELETE, and more.
The $http service returns a promise, which allows you to handle asynchronous data in a more effective way. You can use this promise to process the data returned by the server or to handle errors that may occur during the HTTP request.
Some common use cases for the $http service include fetching data from a server, submitting form data to a server, and updating data on a server. With the help of $http, you can easily interact with external data sources and make your AngularJS applications more dynamic and powerful.
How to make a GET or POST request using $http service in Angular.js?
To make a GET or POST request using $http service in AngularJS, you need to follow the below steps:
Inject the $http service into your controller, service or factory.myApp.controller(‘myController’, function($http) {
// Controller code goes here
});Use the $http service to make the request. For GET requests, use the
get()method and for POST requests, use thepost()method. Both methods take two parameters – the URL to which the request is to be made and an optional configuration object.// GET request
$http.get(‘/api/data’).then(function(response) {
// success callback
console.log(response.data);
}, function(error) {
// error callback
console.log(error);
});// POST request
$http.post(‘/api/data’, {name: ‘John’, age: 25}).then(function(response) {
// success callback
console.log(response.data);
}, function(error) {
// error callback
console.log(error);
});In the above example, we are making a GET request to the
/api/dataURL and a POST request to the same URL with a JSON object containing name and age properties.Handle the response using promises. The
$httpservice returns a promise object that allows you to handle the response in a more efficient way. Thethen()method is used to handle both success and error responses.$http.get(‘/api/data’).then(function(response) {// success callback
console.log(response.data);
}, function(error) {
// error callback
console.log(error);
});In the above example, we are using the
then()method to handle the response. If the request is successful, the success callback function will be called, and if there is an error, the error callback function will be called.
That’s how you can make GET or POST requests using the $http service in AngularJS.
function($http) {
// Controller code goes here
});Use the $http service to make the request. For GET requests, use the get() method and for POST requests, use the post() method. Both methods take two parameters – the URL to which the request is to be made and an optional configuration object.
// GET request
$http.get('/api/data').then(function(response) {
// success callback
console.log(response.data);
}, function(error) {
// error callback
console.log(error);
});
// POST request
$http.post('/api/data', {name: 'John', age: 25}).then(function(response) {
// success callback
console.log(response.data);
}, function(error) {
// error callback
console.log(error);
});In the above example, we are making a GET request to the /api/data URL and a POST request to the same URL with a JSON object containing name and age properties.
2. Handle the response using promises. The $http service returns a promise object that allows you to handle the response in a more efficient way. The then() method is used to handle both success and error response
$http.get('/api/data').then(function(response) {
// success callback
console.log(response.data);
}, function(error) {
// error callback
console.log(error);
});In the above example, we are using the then() method to handle the response. If the request is successful, the success callback function will be called, and if there is an error, the error callback function will be called.
That’s how you can make GET or POST requests using the $http service in AngularJS.
What are the advantages of using the $resource service over $http in Angular.js?
The $resource service in AngularJS is a higher-level abstraction on top of the $http service, which makes it easier to interact with RESTful APIs. Here are some advantages of using the $resource service over the $http service in AngularJS:
Higher-level abstraction: The $resource service provides a higher-level abstraction for interacting with RESTful APIs, which means that you don’t have to write as much code as you would with the $http service. With $resource, you can define a resource object that represents a RESTful endpoint and then use its methods to perform CRUD operations.
Simplified syntax: The syntax for using $resource is simpler and more intuitive than that of $http. For example, to make a GET request using $http, you need to write a lot of code to handle success and error callbacks. With $resource, you can simply call the
query()method to get a list of resources, orget()method to retrieve a single resource.Data modeling: With $resource, you can easily model your data using the resource object, which makes it easier to handle complex data structures. You can define custom methods on the resource object to perform more complex operations on your data.
Caching: $resource provides built-in caching support, which allows you to cache responses from your API for faster access. This can be useful in scenarios where you need to fetch the same data multiple times.
Type safety: $resource provides type safety, which means that you can define the expected response type for each resource. This makes it easier to handle errors and to work with data in a more structured way.
In summary, the $resource service provides a more abstract and simplified way of interacting with RESTful APIs compared to the $http service in AngularJS. It provides a more intuitive syntax, data modeling, caching, and type safety, which can make your code more maintainable and easier to work with.
Explain the difference between Promise and Observable in Angular.js when making HTTP requests?
Both Promise and Observable are used for handling asynchronous operations in AngularJS, including HTTP requests. However, there are some key differences between these two approaches:
Execution: A Promise is executed immediately when it is created, whereas an Observable is lazy and doesn’t start executing until it is subscribed to.
Handling: A Promise can only handle a single value or error, whereas an Observable can handle multiple values over time.
Cancellation: A Promise cannot be cancelled once it is created, whereas an Observable can be cancelled at any time by unsubscribing from it.
Operators: Observables have a rich set of operators such as map, filter, reduce, debounceTime, and more that allow you to transform, filter, and combine data streams. Promises don’t have such operators.
Error handling: Promises use a catch method for handling errors, whereas Observables have an error callback for handling errors.
When making HTTP requests, both Promise and Observable can be used to handle the response. The $http service in AngularJS returns a Promise by default, but it also supports Observables through the fromPromise() method. You can use either of these approaches depending on your use case.
For example, if you only need to make a single HTTP request and handle the response or error once, then using a Promise might be sufficient. On the other hand, if you need to handle multiple responses over time, perform advanced transformations on the data, or cancel the request, then using an Observable might be a better fit.
In summary, while both Promise and Observable are used for handling asynchronous operations in AngularJS, they have different execution models, handling capabilities, cancellation mechanisms, and operators, which make them suitable for different use cases.
How to handle errors in Angular.js HTTP requests?
In AngularJS, errors in HTTP requests can be handled in different ways, depending on the specific requirements of your application. Here are some common approaches:
Using Promises: When using the $http service in AngularJS, the
then()method can be used to handle both successful responses and errors. Thethen()method takes two callbacks as arguments – one for handling successful responses, and another for handling errors. Here’s an example:
$http.get('/api/data')
.then(function(response) {
// handle successful response
}, function(error) {
// handle error
});2. Using Observables: When using Observables, you can use the catch() method to handle errors. The catch() method takes a callback function that handles errors. Here’s an example:
mport { catchError } from 'rxjs/operators';
import { Observable } from 'rxjs/Observable';
this.http.get('/api/data')
.pipe(
catchError((error: any) => {
// handle error
return Observable.throw(error);
})
)
.subscribe((response: any) => {
// handle successful response
});3. Handling errors globally: You can handle errors globally by registering an interceptor that intercepts all HTTP requests and responses. This can be useful for handling errors that occur across the application, such as network errors or authentication errors. Here’s an example:
In this example, we define an interceptor that intercepts all HTTP responses with an error status code (i.e. 4xx or 5xx). The responseError method is called when an error occurs, and we can handle the error in this method. We then return a rejected promise to propagate the error to the caller.
In summary, errors in AngularJS HTTP requests can be handled using Promises or Observables, and can be handled locally or globally using interceptors.
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