JavaScript Foundations 1

What keyword declares a variable that cannot be reassigned?

const

What keyword declares a variable that can be reassigned?

let

What is the default value of an uninitialized variable declared with let?

undefined

What are the primitive data types in JavaScript?

string number boolean undefined null symbol bigint

What operator is used to check the data type of a value?

typeof

What is the result of typeof null?

object (known JavaScript bug)

What is returned by typeof undefined?

undefined

What is the difference between let and var?

let is block scoped var is function scoped

What is string interpolation in JavaScript?

Embedding expressions inside template literals using ${}

What characters define a template literal?

Backticks

What does the ++ operator do?

Increments a value by 1

What is the difference between == and ===?

=== checks value and type == allows type coercion

What does the > operator return?

A boolean indicating if the left value is greater than the right

What is the result type of a comparison expression?

boolean

What is the ternary operator syntax?

condition ? valueIfTrue : valueIfFalse

When should a ternary operator be used?

For simple conditional expressions

What keyword executes code based on a condition?

if

What happens if an if condition is false and there is no else?

The block is skipped

What does console.log() do?

Outputs values to the console

Is JavaScript compiled or interpreted?

Interpreted with JIT compilation

What does JavaScript running in the browser provide access to?

DOM Web APIs browser environment

What does JavaScript dynamic typing mean?

Variable types are determined at runtime and can change

What are the two main categories of data types in JavaScript?

Primitive types and object types

What happens if you declare a variable without let const or var?

It creates a property on the global object (bad practice)

What does NaN stand for?

Not a Number

What is the result of Number('Jonas')?

NaN

What is type conversion in JavaScript?

Explicitly converting one type to another

What is type coercion in JavaScript?

Automatic type conversion performed by JavaScript

Which operator causes string concatenation through coercion?

The + operator

Which operators convert strings to numbers during coercion?

"- * / >

What are the five falsy values in JavaScript?

0 empty string undefined null NaN

Is an empty object truthy or falsy?

Truthy

Why can checking a variable like if(height) be dangerous?

Because 0 is falsy even when it is a valid value

What logical operator represents AND?

&&

What logical operator represents OR?

||

What logical operator negates a boolean value?

!

What keyword prevents a switch case from falling through?

break

What is the default case in a switch statement?

Code that runs if no case matches

What is an expression in JavaScript?

Code that produces a value

What is a statement in JavaScript?

Code that performs an action but does not produce a value

Can statements be used inside template literals?

No only expressions

What engine runs JavaScript in Chrome?

V8

What allows JavaScript to run outside the browser?

Node.js

What does ES6 refer to?

The 2015 major update to JavaScript