Hiring guide for SCALA.js (JavaScript) Engineers

SCALA.js (JavaScript) Developer Hiring Guide

SCALA.js is a JavaScript-based programming language that was developed as a derivative of the SCALA language, designed to run on JavaScript runtime environments. It was created by École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland and officially released in 2015. The main goal of SCALA.js is to allow developers to write their code once and use it both on the server-side (JVM) and client-side (JavaScript). This software offers strong static types, eliminating many common errors at compile-time rather than during execution. Its seamless interoperability with existing JavaScript libraries makes it an efficient tool for web development.

Ask the right questions secure the right SCALA.js (JavaScript) talent among an increasingly shrinking pool of talent.

First 20 minutes

General SCALA.js (JavaScript) app knowledge and experience

The first 20 minutes of the interview should seek to understand the candidate's general background in SCALA.js (JavaScript) application development, including their experience with various programming languages, databases, and their approach to designing scalable and maintainable systems.

What is the use of Option in Scala.js?
Option is a container type in Scala.js used to represent optional values. It can either contain a value (Some) or no value (None). It is used to handle null values and avoid null pointer exceptions.
How would you define a function in Scala.js?
A function in Scala.js can be defined using the 'def' keyword followed by the function name, parameters, return type, and the function body. For example: def add(a: Int, b: Int): Int = { return a + b }
What are case classes in Scala.js?
Case classes in Scala.js are like regular classes but with some additional features. They have an apply method by default which allows us to create instances without using the new keyword. They also have an unapply method which allows for pattern matching.
Describe the difference between val and var in Scala.js.
In Scala.js, 'val' is used to declare a read-only (immutable) variable, meaning once a value is assigned to it, it cannot be changed. On the other hand, 'var' is used to declare a mutable variable, meaning its value can be changed.
How would you handle exceptions in Scala.js?
Exceptions in Scala.js can be handled using try, catch, and finally blocks. The try block contains the code that might throw an exception, the catch block handles the exception, and the finally block contains code that is always executed regardless of an exception.
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What you’re looking for early on

Does the candidate have a clear understanding of SCALA.js?
Has the candidate demonstrated problem-solving skills?
Is the candidate familiar with JavaScript and its frameworks?
Can the candidate work well in a team?

Next 20 minutes

Specific SCALA.js (JavaScript) development questions

The next 20 minutes of the interview should focus on the candidate's expertise with specific backend frameworks, their understanding of RESTful APIs, and their experience in handling data storage and retrieval efficiently.

What are implicit parameters in Scala.js?
Implicit parameters in Scala.js are parameters that are passed to a function automatically by the compiler when they are not provided explicitly. They are defined using the 'implicit' keyword.
How would you use Futures in Scala.js?
Futures in Scala.js are used to perform asynchronous operations. A Future is a placeholder object for a value that may not yet exist. It is created by passing a code block to the Future object. The result can be retrieved using methods like onComplete, onSuccess, and onFailure.
Describe the difference between a sequence and a list in Scala.js.
In Scala.js, a sequence (Seq) is a general interface for data structures that have a defined order of elements. A list is a specific implementation of a sequence that represents a linked list. Lists are best when you want to add or remove elements at the head, while sequences are better for random access.
What is pattern matching in Scala.js?
Pattern matching in Scala.js is a powerful feature that allows you to match on the structure of data and extract values. It is similar to switch statements in other languages but more powerful. It can match on types, values, and even complex structures.
How would you create a singleton object in Scala.js?
In Scala.js, a singleton object is created using the 'object' keyword instead of the 'class' keyword. This creates a single instance of the object that can be accessed directly without needing to create a new instance.
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The ideal back-end app developer

What you’re looking to see on the SCALA.js (JavaScript) engineer at this point.

At this point, a skilled SCALA.js (JavaScript) engineer should demonstrate strong problem-solving abilities, proficiency in SCALA.js (JavaScript) programming language, and knowledge of software development methodologies. Red flags include lack of hands-on experience, inability to articulate complex concepts, or unfamiliarity with standard coding practices.

Digging deeper

Code questions

These will help you see the candidate's real-world development capabilities with SCALA.js (JavaScript).

What does the following Scala.js code do?
def add(a: Int, b: Int): Int = a + b
This code defines a function named 'add' that takes two integer parameters, 'a' and 'b'. It returns the sum of 'a' and 'b'.
What will be the output of the following Scala.js code?
val list = List(1, 2, 3, 4, 5)
list.map(_ * 2)
This code will output a new list with each element multiplied by 2. So, the output will be List(2, 4, 6, 8, 10).
What does the following Scala.js code do?
val list = List(1, 2, 3, 4, 5)
list.reduce(_ + _)
This code reduces the list by applying the function provided, which is addition in this case. So, it adds up all the elements in the list and returns the sum, which is 15.
What does the following Scala.js code do?
import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.Future
val future = Future { Thread.sleep(5000); 42 }
This code creates a Future that will complete with the value 42 after a delay of 5 seconds. Futures in Scala are a way of creating a value that will be available at some point in the future, allowing for non-blocking, asynchronous programming.

Wrap-up questions

Final candidate for SCALA.js (JavaScript) Developer role questions

The final few questions should evaluate the candidate's teamwork, communication, and problem-solving skills. Additionally, assess their knowledge of microservices architecture, serverless computing, and how they handle SCALA.js (JavaScript) application deployments. Inquire about their experience in handling system failures and their approach to debugging and troubleshooting.

What are higher-order functions in Scala.js?
Higher-order functions in Scala.js are functions that can take other functions as parameters and/or return functions as results. They are a key feature of functional programming and allow for powerful abstractions.
Describe the difference between a trait and an abstract class in Scala.js.
In Scala.js, both traits and abstract classes can have abstract and concrete methods. The main difference is that a class can extend multiple traits but only one abstract class. Also, traits cannot have constructor parameters while abstract classes can.
How would you use the 'for' comprehension in Scala.js?
The 'for' comprehension in Scala.js is a syntactic sugar for chaining multiple operations like map, flatMap, and filter. It is used to write more readable code when dealing with multiple operations on collections or other monadic types.

SCALA.js (JavaScript) application related

Product Perfect's SCALA.js (JavaScript) development capabilities

Beyond hiring for your SCALA.js (JavaScript) engineering team, you may be in the market for additional help. Product Perfect provides seasoned expertise in SCALA.js (JavaScript) projects, and can engage in multiple capacities.