Strict null checks and safety in Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does enabling strictNullChecks in TypeScript do?

It makes TypeScript treat null and undefined as distinct types that must be explicitly handled, preventing accidental errors from uninitialized or missing values.

beginner

How do you safely access a property of an object that might be null or undefined in TypeScript with strict null checks?

You can use the optional chaining operator ?. to safely access properties without causing runtime errors if the object is null or undefined.

beginner

What is a common way to provide a fallback value when a variable might be null or undefined?

Use the nullish coalescing operator ?? to provide a default value only when the variable is null or undefined.

intermediate

Why is it safer to enable strictNullChecks compared to having it disabled?

Because it forces you to handle null and undefined explicitly, reducing bugs caused by unexpected missing values and improving code reliability.

beginner

What TypeScript type can represent a variable that might be a string or might be null?

You can use a union type like string | null to explicitly say the variable can hold either a string or null.

What happens if you try to assign null to a variable of type string with strictNullChecks enabled?

A TypeScript shows an error.

B It works without any error.

C The variable becomes <code>undefined</code>.

D The code compiles but throws a runtime error.

With strictNullChecks enabled, null is not assignable to string unless explicitly allowed.

Which operator safely accesses a property of an object that might be null or undefined?

A ??

B !!

C ?.

D ||

The optional chaining operator ?. safely accesses properties without errors if the object is null or undefined.

What does the nullish coalescing operator ?? do?

A Throws an error if the value is <code>null</code>.

B Returns the right value if the left is falsy.

C Checks if a value is <code>null</code>.

D Returns the right value if the left is <code>null</code> or <code>undefined</code>.

The ?? operator returns the right side only if the left side is null or undefined.

Which TypeScript setting enables strict null checks?

A strictNullChecks

B noImplicitAny

C noUnusedLocals

D allowJs

The strictNullChecks compiler option enables strict checking of null and undefined.

If a variable is declared as string | null, what must you do before using it as a string?

A Use it directly without checks.

B Check if it is not <code>null</code>.

C Assign it to <code>undefined</code>.

D Convert it to a number.

You must check the variable is not null before using it as a string to avoid errors.

Explain how strictNullChecks improves safety in TypeScript code.

Think about how TypeScript treats missing values with this setting.

Describe how to safely access a property of an object that might be null or undefined.

Consider the operator that stops property access if the object is missing.