We also had included several TypeScript Code Challenges that will help you to be more prepared for your interview ahead. So when you had mastered our selection, you will be ready to excel in your TypeScript interview.
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Basic TypeScript questions
It has better IDE Support: There is a wide range of IDEs with excellent support for TypeScript, like Atom, IntelliJ/WebStorm, Sublime, or Visual Studio & VS code.
It let us use new features of ECMAScript: TypeScript supports ECMAScript standards and transpile them to ECMAScript targets.
Does TypeScript have any disadvantages?
Mention the types of components in TypeScript
There are three types of components in TypeScript:
The Language: the syntax, keywords, and type annotations.
The TypeScript Language Service: it supports the common set of typical editor operations and exposes an additional layer around the core compiler pipeline, editor-like applications.
What are the types of TypeScript?
The Type System represents the different types of values supported by TypeScript, which checks the validity of the supplied values previously to do any manipulation or data storage by the program. Type can be classified as a) Built-in that includes boolean, null, number, string, undefined, void, and b) User-defined, which includes arrays, classes, enumerations (enums), interfaces, and tuple.
What are Variables in TypeScript?
Variables are named spaces in the memory, used to store values. The syntax for declaring a variable in TypeScript includes a colon (:) after the variable name, and then its type.
Mention the object-oriented terms supported by TypeScript
TypeScript supports the object-oriented terms Classes, Data Types, Inheritance, Interfaces, Member functions, and Modules.
What are Classes in TypeScript?
What are loops in TypeScript?
A loop allows repeating the execution of a statement or a series of statements. In TypeScript the following types of loops are implemented:
For Loop: it is a definite loop with a fixed number of iterations.
While Loop: when the supplied condition turns to be true, the while loop executes the given instructions.
Do..While Loop: this loop acts like to the while loop, except that the condition isn't evaluated the first time the loop runs.
How to create objects in Typescript?
Objects are collections of one-of-a-kind keys and values that resemble a dictionary. Keys resemble arrays and are referred to as associative arrays. An array, on the other hand, employs numbers to index the values.
Therefore, an object lets you use any type as the key. Therefore, an Object type in TypeScript refers to any value with properties and can be defined by specifying the properties and kinds of those properties.
What is contextual typing?
When one side of the equation has a type but the other does not, the TypeScript compiler determines the whole form for us. That way, we don’t need to spend time writing that part of the code, since TypeScript will figure it out for us.
Advanced TypeScript interview questions
Mixin is a way of building up classes from reusable components and then building them by combining simpler partial classes. Instead of a class A extending class B to get its functionality, function B takes class A. Then, it returns a new class with this added functionality, where function B is a mixin.
Explain how TypeScript supports optional parameters in a function
TypeScript compiler flag an error when we try to invoke a function without providing the exact number and types of parameters, as declared in its function signature. A way to surpass this difficulty is to use optional parameters, introduced by a question mark sign (‘?’). This tells the compiler that the parameters may or may not receive a value that can be appended as optional.
What is TypeScript Declare Keyword?
Explain what are Generics in TypeScript
TypeScript Generics is a tool to create reusable components that can work with several data types, rather than a single data type. It also provides type safety without compromising the performance, or productivity. In generics, the type parameter is written between the open (<) and close (>) brackets.
Generics allow us to create generic classes, functions, methods, and interfaces.
What is Enum in TypeScript?
Enums stand for enumerations: a TypeScript data type that let us define a set of named constants, a collection of related values that can be numeric or string values. It makes it easier to document intent or create a set of distinct cases.
Explain the use of the Rest parameters
The rest parameter is used to pass zero or more values to a function. We declare it by prefixing the three-dot characters (‘…’) before the parameter and allowing the functions to have a variable number of arguments without using the arguments object. The rest parameter is useful where we have an undetermined number of parameters.
However, there are some rules to follow in the rest parameter. We can have only one rest parameter per function and it must be an array type, as well as it must be the last parameter in the parameter list.
What are Type assertions in TypeScript?
Type assertions are similar to typecasting in other languages but without type checking or restructuring of data like in C# or Java. Typecasting comes with runtime support, meanwhile, type assertion has no impact on runtime. However, type assertion can be used by the compiler to provide hints on how we want the code to be analyzed.
What are ambient declarations in TypeScripts?
If these source codes are absent at runtime and are invoked, the run will break without warning. Those ambient declarations files are like docs files, so if the source changes, the docs need to be updated or compiler errors will occur.
What is JSX in TypeScript?
In order to use JSX in our code, we need to inject it through a file with a .tsx extension and enable the jsx option. Then, we can use one of the three JSX modes in TypeScript:
The preserve mode: it keeps the JSX as part of the output to be further used in another transform step. The output will have a .jsx file extension as well.
The react mode: it emits React.createElement, does not need to go through a JSX transformation to use it, and the output will have a .js file extension.
The react-native mode: is the equivalent of the preserve and keeps all JSX, but the output has a .js file extension.
How TypeScript files can be supported from Node Modules?
These can be done in TypeScript with a feature similar to @types/ support, to override a specific built-in lib. It will check for a scoped @typescript/lib-* package in node modules to select which lib files to include. Then, the package manager should be used to install the specific package to take over for our particular library.
What is a TypeScript Map file?
TypeScript Code Challenges
With these challenges, we have reached the end of this article on TypeScript Interview Questions. We hope that you feel now more confident and remember: make sure you study and practice as much as possible. Good luck with that interview ahead!
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