Why union types are needed in Typescript - Quick Recap

Recall & Review

beginner

What is a union type in TypeScript?

A union type allows a variable to hold values of different types, like a choice between multiple types.

beginner

Why do we need union types instead of just one type?

Because sometimes a value can be more than one type, like a number or a string, and union types let us handle that safely.

intermediate

How do union types help prevent errors?

They make sure you only use the allowed types and force you to check which type you have before using it, avoiding mistakes.

beginner

Give an example of a union type in TypeScript.

Example: let value: number | string; means value can be a number or a string.

beginner

What real-life situation is similar to union types?

Like a key that can open either your house or your car. You have one key but it works for two things, just like one variable can hold two types.

What does a union type allow in TypeScript?

A No types at all

B A variable to hold multiple types

C Only one fixed type

D Only string types

Union types let variables hold values of more than one type.

Which symbol is used to define a union type?

A |

B ;

C :

D &

The pipe symbol | is used to separate types in a union.

Why should you check the type of a union variable before using it?

A To avoid runtime errors

B To make code slower

C To ignore type safety

D To delete the variable

Checking type ensures you use the variable correctly and avoid errors.

Which of these is a valid union type declaration?

A let x: number & string;

B let x: number string;

C let x: number | string;

D let x: number/string;

The correct syntax uses | to separate types.

What problem do union types solve?

A Forcing variables to be undefined

B Making variables only one type

C Removing types completely

D Allowing variables to hold multiple possible types

Union types let variables hold values of different types safely.

Explain why union types are useful in TypeScript with an example.

Think about variables that can hold more than one type.

Describe how union types help prevent errors in your code.

Consider what happens if you use a variable without knowing its type.