Unlocking the Secrets of Library Interview Questions: A Comprehensive Guide

Submit an interview question

Questions and answers sent in will be looked over and edited by Toptal, LLC, and may or may not be posted, at their sole discretion.

Toptal sourced essential questions that the best web developers can answer. Driven from our community, we encourage experts to submit questions and offer feedback.

What is CORS? How does it work?

Cross-origin resource sharing (CORS) is a mechanism that allows many resources (e.g., fonts, JavaScript, etc.) on a web page to be requested from another domain outside the domain from which the resource originated. It’s a mechanism supported in HTML5 that manages XMLHttpRequest access to a domain different.

CORS adds new HTTP headers that provide access to permitted origin domains. For HTTP methods other than GET (or POST with some MIME types), the specification says that browsers must first use an HTTP OPTIONS request header to ask the server for a list of supported methods. The actual request can then be submitted. Servers can also notify clients whether “credentials” (including Cookies and HTTP Authentication data) should be sent with requests. 2 .

Explain the purpose of each of the HTTP request types when used with a RESTful web service.

When used with a RESTful web service, each of the HTTP request types is used for the following:

• GET: Gets information from the server; it should only get information and not do anything else.
• POST: Sends data to the server for a new entity. It is often used to send a completed web form or upload a file.
• PUT is like POST, but it’s used to replace an existing object.
• PATCH is like PUT, but it’s used to change only certain fields in an existing entity.
• DELETE: Removes data from the server.
• TRACE lets you check what each machine on the network path gets when you send a request. As such, it simply returns what was sent.
• Options: This lets a client ask for information about the request methods a service supports. Allow is the response header that matters, and it just lists the methods that are supported. It can also be used to find out what kinds of requests the server where the service is located can handle by adding a * to the URI. ).
• HEAD is the same as the GET method for a resource, but it only sends back the response headers. e. , with no entity-body).
• CONNECT: This method is mostly used to connect to a resource over the network, usually through a proxy that can be asked to forward an HTTP request as TCP and keep the connection going. It sends a 200 status code and a message that says “Connection Established” once the connection is made.

3 .

Describe the key advantages of HTTP/2 as compared with HTTP 1.1.

HTTP/2 provides decreased latency to improve page load speed by supporting:

• Data compression of HTTP headers
• Server push technologies
• Page elements can be loaded at the same time over a single TCP connection.
• Prioritization of requests

An important operational benefit of HTTP/2 is that it avoids the head-of-line blocking problem in HTTP 1.

Apply to Join Toptals Development Network

and enjoy reliable, steady, remote Freelance Web Developer Jobs

Explain the basic structure of a MIME multipart message when used to transfer different content type parts. Provide a simple example.

A simple example of a MIME multipart message is as follows:

Each MIME message starts with a message header. This header contains information about the message content and boundary. In this case, Content-Type: multipart/mixed; boundary=frontier means that the message is made up of several parts, each with its own content type and a boundary of –frontier between them.

Each part consists of its own content header (zero or more Content- header fields) and a body. Multipart content can be nested. To keep things simple, a multipart type’s content-transfer-encoding can only be 7bit, 8bit, or binary. Multiple levels of decoding would be too hard to handle. As a whole, the multipart block doesn’t have a charset. The Encoded-Word system handles non-ASCII characters in the part headers, and charsets can be set for the part bodies if it makes sense for their content type. 5 .

What is long polling, how does it work, and why would you use it? What is the biggest problem with long polling in terms of server and client resources? What is the best HTML5 feature that can be used instead of long polling?

HTTP is based on a pattern of requests and responses. This means that the server can’t send data to the client (i.e. e. , the server can only provide data to the client in response to a client request). Long polling is a web application development pattern used to emulate pushing data from server to client. The client sends a request to the server using the long polling pattern. The connection stays open until the server is ready to send data to the client. The connection is closed only after data is sent back to the client or connection timeout occurs. The client then creates a new request when the connection is closed, thus restarting the loop.

There are two important drawbacks that need to be considered when using long polling:

• There is no difference between long polling requests and other HTTP requests, so web servers handle them in the same way. That’s right, each long poll connection will take up server resources, which could limit the number of connections the server can handle. This can lead to HTTP connection timeouts.
• There is a limit on how many connections a web app can make in each web browser. This means that your app may take longer to load and work less well.

In HTML5, a useful alternative to long polling is using a WebSocket. A WebSocket is a protocol providing full-duplex communications channels over a single TCP connection. The WebSocket protocol lets a browser and a website talk to each other more, which allows for live content and gets rid of the need for long polling.

Another potential answer could be Server-sent DOM Events. Which is method of continuously sending data from a server to the browser, rather than repeatedly requesting it. However, this HTML5 feature is not supported by Microsoft Internet Explorer, thus making it less attractive solution. 6 .

Consider the following JavaScript code that is executed in a browser:

If executeAjaxCallAsync() uses a standard XmlHttpRequest to get data from the server asynchronously, how many HTTP requests do you think this loop will make at the same time?

Number of concurrent HTTP requests and XmlHttpRequest is limited in all browsers. Specific limitations are different depending on browser type and version.

For example, according to Mozilla Developer Network Firefox 3 limits the number of XMLHttpRequest connections per server to 6 (previous versions limit this to 2 per server).

After thinking about this, the browser would run this loop in chunks so that the number of HTTP requests it creates at the same time would never be more than 6. 7 .

What is an ETag and how does it work?

An ETag is a unique number that a web server gives to a certain version of a resource that can be found at a URL. If the resource content at that URL ever changes, a new and different ETag is assigned.

When a URL is requested, the web server usually sends back the resource along with its ETag value. This value is stored in an HTTP “ETag” field:

The client may then decide to cache the resource, along with its ETag. The client will send its saved copy of the ETag along with the request in an “If-None-Match” field the next time it wants to get the same URL.

When the client makes a new request, the server may now check the ETag against the ETag for the most recent version of the resource. The server may send back a very short response with an HTTP 304 Not Modified status if the ETag values match. This means that the resource has not changed. The client knows that its cached copy is still good when it sees the 304 status.

The resource has probably changed, though, if the ETag values don’t match. A full response with the resource’s content is sent back, just like if ETag weren’t being used. If this happens, the client may choose to replace the version it had cached with the new resource and ETag. 8 .

Explain the difference between stateless and stateful protocols. Which type of protocol is HTTP? Explain your answer.

A stateless communications protocol treats each request as an independent transaction. Because of this, the server doesn’t have to keep any session, identity, or status information for multiple requests from the same source. Similarly, the requestor can not rely on any such information being retained by the responder.

A stateful communications protocol, on the other hand, keeps “state” information like session data, identity, status, etc., on the responding party. ) across multiple requests from the same source.

HTTP is a stateless protocol. HTTP doesn’t require servers to keep track of information or status about each user for as long as the requests last.

Some web servers implement states using different methods (using cookies, custom headers, hidden form fields etc. ). Though, HTTP is what all web apps depend on at their core. HTTP is still a stateless protocol based on the simple request/response paradigm. 9 .

In your words, what is a “MIME type,” what does it contain, and what is it used for?

MIME is an acronym for Multi-purpose Internet Mail Extensions. It is used as a standard way of classifying file types over the Internet.

Web servers and browsers both have a list of MIME types that make it easy to send files of a known type to other computers or browsers.

There are two parts to a MIME type: a type and a subtype. A slash (/) separates them. For example, the MIME type for Microsoft Word files is application/msword (i. e. , type is application and the subtype is msword). 10 .

What’s the difference between GET and POST?

Both are methods used in HTTP requests. Generally it is said that GET is to download data and PUT is to upload data. But we can do both downloading as well as uploading either by GET/POST.

• When we send parameters to the server in a GET request, those parameters will show up in the URL because parameters are added to the end of the URL in GET. So there’s no safety when you upload to the server.
• Due to the URL’s maximum size, we can only send a certain amount of data in a GET request. We also can’t add a long data string to the URL.

• The parameters we send in the body of a request when we use POST are To make things safer, we should encrypt the data we send in the body of an HTTP request.
• We can send a lot more data using POST.

Note: GET is faster when we only need to get data from a static API call and don’t need to pass any parameters.

There is more to interviewing than tricky technical questions, so these are intended merely as a guide. Not every good candidate for the job will be able to answer all of them, and answering all of them doesn’t mean they are a good candidate. At the end of the day, hiring remains an art, a science — and a lot of work.

Tired of interviewing candidates? Not sure what to ask to get you a top hire?

Let Toptal find the best people for you.

Our Exclusive Network of Web Developers

Looking to land a job as a Web Developer?

Let Toptal find the right job for you.

Job Opportunities From Our Network

How to Answer Behavioral Interview Questions Sample Answers