Web Interview Questions
1. What is AJAX? How does it work?
AJAX(Asynchronous Javascript And XML) uses a combination of technologies to load content on the web-page dynamically without a full reload:
- HTML and CSS for marking up and styling information.
- The DOM accessed with JavaScript to dynamically display and interact with the information presented.
- A method for exchanging data asynchronously between browser and server, thereby avoiding page reloads. The XMLHttpRequest (XHR) object is usually used, but sometimes an IFrame object or a dynamically added tag is used instead.
- A format for the data sent to the browser. Common formats include XML, pre-formatted HTML, plain text, and JavaScript Object Notation (JSON). This data could be created dynamically by some form of server-side scripting.
2. What is CORS? How does it work? What is preflight?
Cross-Origin Resource Sharing (CORS) is a web browser security feature that controls how web applications at one origin can interact with resources at a different origin. It is an integral part of the browser’s security model, enforcing the same-origin policy which restricts documents or scripts from different origins from accessing each other’s resources.
How Does CORS Work?
CORS involves a set of steps and checks performed by both the browser and the server:
- Browser’s Check: When a page requests a resource from a different origin, the browser first checks the CORS policy of that resource.
- Server’s Response: The server hosting the resource responds with specific CORS headers, such as
Access-Control-Allow-Origin, indicating whether the resource is accessible.
- Conditional Access: If the server’s CORS policy allows the request, the browser proceeds with loading the resource. Otherwise, the request is blocked.
What is Preflight in CORS?
Preflight is a CORS process used for validating certain types of cross-origin requests before the actual request is made:
- Definition: Preflight is an additional step in CORS that is used for certain types of cross-origin requests.
- Purpose: Preflight requests are sent to the server to determine if the actual request is safe to send. It’s like asking for permission or a “green light” before the actual request.
- Trigger: Preflight requests are typically triggered by HTTP requests that use methods other than GET, HEAD, or POST, or that use POST with certain MIME types, or that include custom headers.
- Process: The preflight request is an HTTP OPTIONS request sent to the server hosting the other-origin resource. This request includes headers like Access-Control-Request-Method and Access-Control-Request-Headers that inform the server about the method and headers of the actual request.
- Server Response: If the server responds to the preflight request with appropriate CORS headers that approve the request’s method and headers, the browser proceeds to send the actual request.
3. What are cookies? How does it work?
Best answer ever! - https://stackoverflow.com/a/48654382/2109394
4. Which are the 5 groups of HTTP codes? What do we use them for?
- Informational responses (100 – 199)
- Successful responses (200 – 299)
- Redirects (300 – 399)
- Client errors (400 – 499)
- Server errors (500 – 599)