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TypeScript Quiz – TypeScript Multiple Choice Questions and Answers
| Quiz Name | TypeScript |
| Exam Type | MCQ (Multiple Choice Questions) |
| Category | Technical Quiz |
| Mode of Quiz | Online |
Practice TypeScript Test Questions | TypeScript MCQ Quiz
Which of the following best describes TypeScript?
a. A programming language
b. A markup language
c. A scripting language
d. A styling language
Answer: a. A programming language
Explanation: TypeScript is a programming language that is a typed superset of JavaScript, designed to make JavaScript development more scalable and maintainable.
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What is the difference between “any” and “unknown” in TypeScript?
a. “Any” is a type that can be assigned any value, while “unknown” is a type that is assigned an unknown value.
b. “Any” is a type that can be assigned any value, while “unknown” is a type that can only be assigned a value after a runtime check.
c. “Any” is a type that can only be assigned a value after a runtime check, while “unknown” is a type that is assigned an unknown value.
d. There is no difference between “any” and “unknown”.
Answer: b. “Any” is a type that can be assigned any value, while “unknown” is a type that can only be assigned a value after a runtime check.
Explanation: The “any” type can be assigned any value without a type check, while the “unknown” type is a type-safe counterpart of “any” and can only be assigned a value after a runtime check or a type assertion.
What is the difference between “interface” and “type” in TypeScript?
a. There is no difference between “interface” and “type”.
b. “Interface” is a keyword for defining object types, while “type” is a keyword for defining any type.
c. “Interface” is a keyword for defining object types with optional properties, while “type” is a keyword for defining object types with required properties.
d. “Interface” is a keyword for defining object types, while “type” is a keyword for defining any type, including object types.
Answer: d. “Interface” is a keyword for defining object types, while “type” is a keyword for defining any type, including object types.
Explanation: Both “interface” and “type” are used to define types in TypeScript, but “interface” is typically used for defining object types, while “type” can be used for any type, including object types.
What is the output of the following TypeScript code?
let x = 5;
x = “hello”;
console.log(x);
a. 5
b. “hello”
c. undefined
d. Error
Answer: d. Error
Explanation: TypeScript is a strongly-typed language, and the variable “x” is declared as a number. Assigning a string value to a variable of type number results in a type error.
What is the difference between “public” and “private” access modifiers in TypeScript?
a. “Public” members can only be accessed within their own class, while “private” members can be accessed from any class.
b. “Public” members can be accessed from any class, while “private” members can only be accessed within their own class.
c. “Public” and “private” are not valid access modifiers in TypeScript.
d. There is no difference between “public” and “private” access modifiers in TypeScript.
Answer: b. “Public” members can be accessed from any class, while “private” members can only be accessed within their own class.
Explanation: The “public” keyword specifies that a member should be accessible from any location, while the “private” keyword specifies that a member should only be accessible within the defining class.
What is the difference between “readonly” and “const” in TypeScript?
a. There is no difference between “readonly” and “const”.
b. “Readonly” can only be used to declare object properties, while “const” can be used to declare any variable.
c. “Readonly” can only be assigned a value at runtime, while “const” must be assigned a value at compile time.
d. “Readonly” can only be assigned a value once, while “const” can be reassigned multiple times.
Answer: d. “Readonly” can only be assigned a value once, while “const” can be reassigned multiple times.
Explanation: The “readonly” keyword can be used to declare a property that can only be assigned a value once, while the “const” keyword can be used to declare a variable that cannot be reassigned once it has been assigned a value.
What is the difference between “namespace” and “module” in TypeScript?
a. There is no difference between “namespace” and “module”.
b. “Namespace” is an older syntax for organizing code into logical units, while “module” is a newer syntax that is used in modern TypeScript.
c. “Namespace” is used for client-side code, while “module” is used for server-side code.
d. “Namespace” is used for internal code organization, while “module” is used for external code organization.
Answer: b. “Namespace” is an older syntax for organizing code into logical units, while “module” is a newer syntax that is used in modern TypeScript.
Explanation: “Namespace” and “module” are used to organize code in TypeScript, but “module” is the recommended way of organizing code in modern TypeScript projects.
What is the purpose of the “as” keyword in TypeScript?
a. To declare a variable as a constant.
b. To cast a variable to a different type.
c. To declare a variable as an object.
d. To declare a variable as a function.
Answer: b. To cast a variable to a different type.
Explanation: The “as” keyword is used for type assertions in TypeScript, which allows you to cast a variable to a different type.
What is the output of the following TypeScript code?
const foo = (): number => 5;
console.log(foo());
a. 5
b. “5”
c. undefined
d. Error
Answer: a. 5
Explanation: The arrow function “foo” returns the number 5, which is logged to the console using the “console.log” method.
What is the difference between “abstract” and “interface” in TypeScript?
a. “Abstract” is used to define concrete classes, while “interface” is used to define abstract classes.
b. “Abstract” is used to define abstract classes, while “interface” is used to define concrete classes.
c. “Abstract” and “interface” are not valid keywords in TypeScript.
d. There is no difference between “abstract” and “interface” in TypeScript.
Answer: b. “Abstract” is used to define abstract classes, while “interface” is used to define concrete classes.
Explanation: “Abstract” is used to define abstract classes that cannot be instantiated, while “interface” is used to define contracts that classes can implement to ensure they have certain properties and methods.
What is the purpose of the “never” type in TypeScript?
a. To declare a variable that can be assigned any value.
b. To declare a variable that cannot be reassigned once it has been assigned a value.
c. To declare a function that never returns.
d. To declare a function that always returns.
Answer: c. To declare a function that never returns.
Explanation: The “never” type is used to declare a function that never returns, such as a function that throws an error or enters an infinite loop.
What is the difference between “undefined” and “null” in TypeScript?
a. There is no difference between “undefined” and “null” in TypeScript.
b. “Undefined” is used to indicate the absence of a value, while “null” is used to indicate a value that is intentionally empty.
c. “Undefined” is used to indicate a value that is intentionally empty, while “null” is used to indicate the absence of a value.
d. “Undefined” and “null” are both used to indicate a value that is intentionally empty.
Answer: b. “Undefined” is used to indicate the absence of a value, while “null” is used to indicate a value that is intentionally empty.
Explanation: In TypeScript, “undefined” is used to indicate the absence of a value, while “null” is used to indicate a value that is intentionally empty.
What is the difference between “private” and “protected” in TypeScript?
a. There is no difference between “private” and “protected” in TypeScript.
b. “Private” properties can only be accessed within the same class, while “protected” properties can also be accessed in subclasses.
c. “Private” properties can be accessed within the same class and in subclasses, while “protected” properties can only be accessed within the same class.
d. “Private” and “protected” are both used to declare properties that can be accessed from anywhere in the code.
Answer: b. “Private” properties can only be accessed within the same class, while “protected” properties can also be accessed in subclasses.
Explanation: In TypeScript, “private” properties can only be accessed within the same class, while “protected” properties can also be accessed in subclasses.
What is the difference between “typeof” and “instanceof” in TypeScript?
a. There is no difference between “typeof” and “instanceof” in TypeScript.
b. “typeof” is used to check the type of a variable at runtime, while “instanceof” is used to check if an object is an instance of a specific class.
c. “typeof” is used to check if an object is an instance of a specific class, while “instanceof” is used to check the type of a variable at runtime.
d. “typeof” and “instanceof” are both used to check the type of a variable at runtime.
Answer: b. “typeof” is used to check the type of a variable at runtime, while “instanceof” is used to check if an object is an instance of a specific class.
Explanation: The “typeof” operator is used to check the type of a variable at runtime, while the “instanceof” operator is used to check if an object is an instance of a specific class.
What is the difference between “super” and “this” in TypeScript?
a. There is no difference between “super” and “this” in TypeScript.
b. “Super” refers to the parent class, while “this” refers to the current instance of a class.
c. “Super” refers to the current instance of a class, while “this” refers to the parent class.
d. “Super” and “this” are both used to refer to the current instance of a class.
Answer: b. “Super” refers to the parent class, while “this” refers to the current instance of a class.
Explanation: In TypeScript, “super” is used to refer to the parent class, while “this” is used to refer to the current instance of a class.
What is the difference between “async” and “await” in TypeScript?
a. There is no difference between “async” and “await” in TypeScript.
b. “Async” is used to mark a function as asynchronous, while “await” is used to wait for the result of an asynchronous function call.
c. “Async” is used to wait for the result of an asynchronous function call, while “await” is used to mark a function as asynchronous.
d. “Async” and “await” are both used to wait for the result of an asynchronous function call.
Answer: b. “Async” is used to mark a function as asynchronous, while “await” is used to wait for the result of an asynchronous function call.
Explanation: In TypeScript, the “async” keyword is used to mark a function as asynchronous, while the “await” keyword is used to wait for the result of an asynchronous function call.
What is the difference between “Array.forEach” and “Array.map” in TypeScript?
a. There is no difference between “Array.forEach” and “Array.map” in TypeScript.
b. “Array.forEach” executes a callback function on each element of an array, while “Array.map” creates a new array by executing a callback function on each element of an existing array.
c. “Array.map” executes a callback function on each element of an array, while “Array.forEach” creates a new array by executing a callback function on each element of an existing array.
d. “Array.forEach” and “Array.map” are both used to execute a callback function on each element of an array.
Answer: b. “Array.forEach” executes a callback function on each element of an array, while “Array.map” creates a new array by executing a callback function on each element of an existing array.
Explanation: In TypeScript, the “Array.forEach” method executes a callback function on each element of an array, while the “Array.map” method creates a new array by executing a callback function on each element of an existing array.
What is the difference between “==” and “===” in TypeScript?
a. There is no difference between “==” and “===” in TypeScript.
b. “==” checks for equality without considering the type, while “===” checks for equality with type consideration.
c. “===” checks for equality without considering the type, while “==” checks for equality with type consideration.
d. “==” and “===” are both used to check for equality without considering the type.
Answer: b. “==” checks for equality without considering the type, while “===” checks for equality with type consideration.
Explanation: In TypeScript, the “==” operator checks for equality without considering the type, while the “===” operator checks for equality with type consideration.
What is the output of the following TypeScript code?
const arr = [1, 2, 3];
const [x, …y] = arr;
console.log(x, y);
a. 1, [2, 3]
b. 1, [1, 2, 3]
c. [1, 2], 3
d. [1, 2, 3], undefined
Answer: a. 1, [2, 3]
Explanation: In the given code, the array “arr” is destructured into two variables, “x” and “y”. The “x” variable is assigned the first element of the array while the “y” variable is assigned the rest of the elements as an array using the spread syntax. Hence, “x” is 1 and “y” is [2, 3], and this is what is printed to the console using the “console.log” statement.
What is the difference between “private” and “protected” access modifiers in TypeScript?
a. There is no difference between “private” and “protected” access modifiers in TypeScript.
b. “Private” members are accessible only within the class where they are defined, while “protected” members are accessible within the class and its subclasses.
c. “Protected” members are accessible only within the class where they are defined, while “private” members are accessible within the class and its subclasses.
d. “Private” members are accessible only within the module where they are defined, while “protected” members are accessible within the class and its subclasses.
Answer: b. “Private” members are accessible only within the class where they are defined, while “protected” members are accessible within the class and its subclasses.
Explanation: In TypeScript, the “private” access modifier restricts the accessibility of a class member to the class where it is defined, while the “protected” access modifier allows the member to be accessed within the class where it is defined as well as its subclasses.
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