What is the difference between let and var?

What will be the output of the following code?

console.log(a); var a = 10;

A). 10

B). undefined

C). Error

D). null

Which of the following is true about variable naming conventions in JavaScript?

A). Variable names can start with a number

B). Variable names are case-insensitive

C). Variable names can include spaces

D). Variable names are case-sensitive

Which keyword should be used to declare a block-scoped variable?

A). var

B). let

C). const

D). Both let and const

Which of the following is true about 'const' variables in JavaScript?

A). They can be redeclared

B). They cannot be reassigned

C). They can be reassigned

D). They are always undefined

Which statement is true about variables in JavaScript?

A). They must be declared before use

B). They can only hold numbers

C). They are statically typed

D). They are strongly typed

What will be the output of the following code?

let a = 1; let b = 2; let c = a + b; console.log(c);

A). 12

B). 12

C). 3

D). NaN

Which keyword is used to declare a variable in JavaScript?

A). var

B). let

C). const

D). All of the above

Which of the following is a valid variable name in JavaScript?

A). 2name

B). _name

C). #name

D).

What will be the output of the following code?

var x = 5; var y = 6; var z = x + y;

A). 11

B). 11

C). 5

D). 6

What will be the output of the following code?

const a = 10; a = 20; console.log(a);

A). 10

B). 20

C). Error

D). undefined