TypeScript Interview Questions

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1. Color Type

TypeScript Arrays OOP Public

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.

(multiple correct answers possible)

Difficulty

Easy

Time

2min

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.

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2. Uppercase Types

TypeScript OOP Types Public

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();

(multiple correct answers possible)

Difficulty

Easy

Time

3min

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.

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3. Positionable

TypeScript Mixins OOP Public

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.

(multiple correct answers possible)

Difficulty

Hard

Time

5min

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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