Optional chaining with types in Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is optional chaining in TypeScript?

Optional chaining is a syntax that allows you to safely access nested object properties without causing an error if a property is null or undefined. It uses the ?. operator.

beginner

How does optional chaining help with types in TypeScript?

It helps by preventing runtime errors when accessing properties that might not exist, and TypeScript understands this to allow safer code with better type checking.

beginner

What will this expression return if user is null? <br>user?.name

It will return undefined instead of throwing an error because optional chaining stops the access if user is null or undefined.

intermediate

Can optional chaining be used with function calls? Give an example.

Yes. For example, obj?.method() calls method only if obj is not null or undefined. Otherwise, it returns undefined.

intermediate

What happens if you use optional chaining on an array element like arr?.[0]?

It safely accesses the first element of arr only if arr is not null or undefined. If arr is null or undefined, it returns undefined without error.

What does the optional chaining operator ?. do in TypeScript?

A Throws an error if the value is null or undefined

B Stops property access if the value is null or undefined and returns undefined

C Always returns null

D Converts the value to a string

Optional chaining stops accessing further properties if the value is null or undefined and returns undefined instead of throwing an error.

Which of these is a valid use of optional chaining?

A user?.address?.street

B user.address?.street

C user?.address.street

D user.address.street?.

Optional chaining must be used before the property you want to safely access, so user?.address?.street is correct.

What will obj?.method() do if obj is undefined?

A Call method and throw error

B Return null

C Call method with undefined context

D Return undefined without calling method

Optional chaining prevents the call if obj is undefined and returns undefined safely.

Can optional chaining be used to safely access array elements?

A Yes, like <code>arr?.[0]</code>

B No, it only works with objects

C Yes, but only with numbers

D No, it causes syntax error

Optional chaining works with arrays using bracket notation, e.g., arr?.[0].

If user is null, what does user?.name ?? 'Guest' return?

A Throws error

B null

C 'Guest'

D undefined

Optional chaining returns undefined for user?.name if user is null, then the nullish coalescing operator ?? returns 'Guest'.

Explain how optional chaining improves safety when accessing nested properties in TypeScript.

Think about what happens if a property is missing or null.

Describe the difference between using optional chaining and normal property access in TypeScript.

Consider what happens when you try to access a property on null or undefined.