Boolean type behavior in Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are the two possible values of a Boolean type in TypeScript?

The Boolean type in TypeScript can only have two values: true or false.

intermediate

How does TypeScript treat non-Boolean values in a Boolean context?

TypeScript uses JavaScript's truthy and falsy rules. Values like 0, '' (empty string), null, undefined, and NaN are treated as false. Others like non-empty strings or numbers (except 0) are true.

beginner

What is the result of Boolean('hello') in TypeScript?

The result is true because non-empty strings are considered truthy.

intermediate

Explain the difference between == and === when comparing Boolean values.

== compares values after type coercion, so 1 == true is true. === compares both value and type, so 1 === true is false. It's best to use === to avoid unexpected results.

beginner

How can you explicitly convert a value to a Boolean in TypeScript?

You can use the Boolean() function or double negation !!value to convert any value to a Boolean.

Which of the following values is considered falsy in TypeScript?

A {}

B 'false'

C []

D 0

0 is falsy. Non-empty strings ('false'), empty arrays ([]), and empty objects ({}) are truthy.

What does the expression !!'0' evaluate to?

A false

B true

C 0

D undefined

The string '0' is non-empty, so it is truthy. Double negation converts it to true.

Which operator checks both value and type equality for Booleans?

A ===

B !=

C ==

D ||

=== checks both value and type equality.

What is the Boolean value of null in TypeScript?

A true

B null

C false

D undefined

null is falsy, so its Boolean value is false.

How do you convert a number to a Boolean explicitly?

A Using <code>Boolean()</code>

B Using <code>Number()</code>

C Using <code>String()</code>

D Using <code>parseInt()</code>

Use Boolean() to convert any value to a Boolean.

Describe how TypeScript treats different values when used in a Boolean context.

Think about which values become true or false when converted.

Explain the difference between == and === when comparing Boolean values in TypeScript.

Focus on how type affects equality.