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TypeScript is an open-source programming language developed and maintained by Microsoft. It is a strict syntactical superset of JavaScript, adding optional static typing to the language. TypeScript is designed for the development of large applications and transcompiles to JavaScript. This means that any existing JavaScript programs are also valid TypeScript programs. One of the key features of TypeScript is its support for static types, which can be used to describe various shapes of JavaScript objects, making it easier to understand and debug code. It also offers features such as classes, modules, and interfaces which provide powerful object-oriented programming capabilities. TypeScript supports definition files that can contain type information of existing JavaScript libraries, much like header files in C/C++. This enables other programs to use the values defined in the files as if they were statically typed TypeScript entities. It has robust tooling support with autocompletion, type inference, and type checking capabilities that can greatly enhance developer productivity. The typescript compiler can convert Typescript (.ts) files into Javascript (.js) files so they can run on any browser or javascript environment. Overall, TypeScript brings scalability and reliability benefits to JavaScript development while maintaining compatibility with existing libraries in the ecosystem.

Ask the right questions secure the right TypeScript talent among an increasingly shrinking pool of talent.

First 20 minutes

General TypeScript app knowledge and experience

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

How would you declare a variable in TypeScript?

You declare a variable in TypeScript using the 'let' or 'const' keyword followed by the variable name. For example, 'let myVar: number;' or 'const myConst: string;'.

What are tuples in TypeScript?

Tuples are a way of storing multiple values in a single variable. They can contain elements of different data types. For example, let myTuple: [string, number] = ['hello', 42];

How do you define an interface in TypeScript?

Interfaces are defined using the 'interface' keyword followed by the interface name and its properties. For example, 'interface User { name: string; age: number; };'

What is the purpose of the 'any' type in TypeScript?

The 'any' type is a powerful way to work with existing JavaScript, allowing you to opt-out of type-checking. It can represent any JavaScript value.

How would you define a class in TypeScript?

You define a class using the 'class' keyword followed by the class name and its properties and methods. For example, 'class MyClass { constructor(public prop: number) {} method() { return this.prop; } };'

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What you’re looking for early on

Does the candidate have a solid understanding of TypeScript's static typing?

Has the candidate demonstrated the ability to work with TypeScript's advanced types?

Can the candidate effectively use TypeScript with popular frameworks like Angular or React?

Is the candidate able to write clean, maintainable code?

Next 20 minutes

Specific TypeScript 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 generics in TypeScript and why are they useful?

Generics provide a way to make components work with any data type and not restrict to one data type. They are useful for creating reusable components.

How would you implement inheritance in TypeScript?

Inheritance is implemented using the 'extends' keyword. For example, 'class ChildClass extends ParentClass { };' This means ChildClass inherits all properties and methods from ParentClass.

Describe the difference between 'interface' and 'type' in TypeScript.

While both 'interface' and 'type' can be used to describe objects, 'interface' is more powerful for defining complex object types. 'type' is more flexible and can represent any valid type, not just objects.

How would you handle errors in TypeScript?

Errors can be handled using try-catch-finally blocks. The 'throw' statement is used to raise custom errors.

What are decorators in TypeScript and how would you use them?

Decorators are a special kind of declaration that can be attached to a class declaration, method, accessor, property, or parameter. They are used to modify or augment the behavior of these elements.

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At this point, a skilled TypeScript engineer should demonstrate strong problem-solving abilities, proficiency in TypeScript 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 TypeScript.

What does the following TypeScript code do?
let x: [string, number];
x = ['hello', 10];
This code declares a tuple type variable 'x' that can hold a string and a number. Then, it assigns the string 'hello' and the number 10 to the tuple.
What will be the output of the following TypeScript code?
let isDone: boolean = false;
console.log(typeof isDone);
This code will output 'boolean' to the console. The 'typeof' operator is used to get the data type of a variable.
What does the following TypeScript code do?
let list: number[] = [1, 2, 3];
let [a, b, c] = list;
console.log(a);
This code creates an array of numbers and then uses array destructuring to assign the array values to the variables 'a', 'b', and 'c'. The console.log statement will output '1'.
What does the following TypeScript code do?
async function asyncCall() {
  let result = await doSomethingAsync();
  console.log(result);
}
This code defines an asynchronous function 'asyncCall'. Inside this function, it waits for the 'doSomethingAsync' function to complete using the 'await' keyword before logging the result to the console.

Wrap-up questions

Final candidate for TypeScript 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 TypeScript application deployments. Inquire about their experience in handling system failures and their approach to debugging and troubleshooting.

How would you define and use an enum in TypeScript?

Enums are a way of giving more friendly names to sets of numeric values. You define them using the 'enum' keyword. For example, 'enum Color {Red, Green, Blue}; let c: Color = Color.Green;'.

Describe the difference between 'null' and 'undefined' in TypeScript.

'null' is an assignment value that means no value or no object. It implies an empty or non-existent value. 'undefined' means a variable has been declared but not assigned a value yet.

What are union types in TypeScript and how would you use them?

Union types are a way to declare a variable that can be one of several types. You define them using the '|' symbol. For example, 'let myVar: number | string;'.

TypeScript application related

Product Perfect's TypeScript development capabilities

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

TypeScript Consultive assessments

TypeScript Application Conversion Assessment TypeScript Application Integration Assessment TypeScript Data & Database Integration Assessment

Custom TypeScript development projects

Custom TypeScript App Conversion TypeScript Custom App Development Process App UI Design for TypeScript Facelifts

Hiring guide for TypeScript Engineers

TypeScript Developer Hiring Guide

What you’re looking for early on

The ideal back-end app developer

What you’re looking to see on the TypeScript engineer at this point.

TypeScript Consultive assessments

Custom TypeScript development projects