Try to solve 3 TypeScript interview questions below. Hints can help you find answers to questions you are having trouble with.
1. Color Type
Arrays
OOP
Arrays
An array is a container of a fixed number of objects of a similar type. It is a fundamental component of most programming languages.
OOP
Object-oriented programming is a paradigm based on encapsulating logic and data into objects, which may then contain fields and procedures. Many of the most widely used programming languages are based on OOP, making it a very important concept in modern programming.
Easy
Easy
The following code initializes three types representing the colors: red, green and blue.
type ColorType = [string, number, number, number];
let red: ColorType = ['Red', 1, 0, 0];
let green: [string, number, number, number] = ['Green', 0, 1, 0];
let blue = ['Blue', 0, 0, 1];
Select the statements that are correct.
(Select all acceptable answers.)
All three colors can have new elements of any type appended to them.
ColorType is an alias to a tuple.
All three colors would compile to the same JavaScript type signature.
ColorType is an array where the type of a fixed number of elements is known.
All three variables are immutable.
2. Uppercase Types
OOP
Types
OOP
Object-oriented programming is a paradigm based on encapsulating logic and data into objects, which may then contain fields and procedures. Many of the most widely used programming languages are based on OOP, making it a very important concept in modern programming.
Types
Many programming languages implement a type system. A type system is a set of constraints that a given variable must obey in order to be considered a predefined type. The main purpose of a type system is to reduce the likelihood of bugs in a computer program. All good developers should be able to work with types.
Easy
Easy
The following code initializes strings as three different types and attempts to make them uppercase. Which statements about the behavior of the typescript compiler are correct?
let stringType: string = "string type";
stringType.toUpperCase();
let anyType: any = "any type";
anyType.toUpper();
anyType.toUpperCase();
let objectType: Object = "object type";
objectType.toUpperCase();(Select all acceptable answers.)
The typescript compiler confirms that toUpperCase exists on the stringType instance.
The typescript compiler states that toUpper does not exist on the anyType instance;
The typescript compiler confirms that toUpperCase exists on the anyType instance.
The typescript compiler states that the toUpperCase function does not exist on the objectType instance.
The typescript compiler confirms that the toUpperCase function exists on the objectType instance.
3. Positionable
Mixins
OOP
Mixins
Mixins are a design pattern that allows classes to be built up from a number of reusable components by combining simpler partial classes. As an increasingly popular design pattern it's important for developers to understand.
OOP
Object-oriented programming is a paradigm based on encapsulating logic and data into objects, which may then contain fields and procedures. Many of the most widely used programming languages are based on OOP, making it a very important concept in modern programming.
Hard
Hard
Consider the following two base classes, Positionable and Rotatable, and MovingObject derived class:
class Positionable {
locationX: number;
locationY: number;
}
class Rotatable {
orientation: number;
rotate(orientation: number) {
this.orientation += orientation;
}
align(rotatable: Rotatable) {
this.orientation = rotatable.orientation;
}
}
class MovingObject implements Positionable, Rotatable {
locationX: number = 0;
locationY: number = 0;
orientation: number = 0;
rotate: (orientation: number) => void;
}
applyMixins(MovingObject, [Positionable, Rotatable]);
function applyMixins(derivedCtor: any, baseCtors: any[]) {
baseCtors.forEach(baseCtor => {
Object.getOwnPropertyNames(baseCtor.prototype).forEach(name => {
derivedCtor.prototype[name] = baseCtor.prototype[name];
});
});
}
let mover = new MovingObject();
mover.rotate(30);
Select the statements that are correct.
(Select all acceptable answers.)
The applyMixins function applies the implementations of Positionable and Rotatable to MovingObject.
The TypeScript compiler will highlight that the property 'align' is missing for the type MovingObject.
As the MovingObject implements Rotatable, the call to mover.rotate(30) will do nothing.
The Positionable class could be changed to an interface without causing any compiler errors.
The properties of MovingObject are required as stand-ins to satisfy the TypeScript compiler.
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