JavaScript Datatypes and Variables

1.		Which of the following is a valid way to concatenate two strings in JavaScript?

str1 .concat(str2)

str1 + str2

str1 - str2

str1 * str2

2.		Which of the following is a valid way to declare and initialize an array with multiple values in JavaScript?

var myArr = [1, 2, 3];

let myArr = {1, 2, 3};

const myArr = [1, 2, 3];

Only A and C

3.		Which of the following is a valid way to check the data type of a variable in JavaScript?

typeof myVar;

myVar.type();

myVar.getType();

typeOf(myVar);

4.		Which of the following is a valid way to declare a variable in JavaScript?

var myVar = 1;

let myVar = 1;

const myVar = 1;

All of the above

5.		Which of the following is a valid way to declare an empty array in JavaScript?

var myArr = [];

let myArr = {};

const myArr = ();

All of the above

6.		What is the result of the following code snippet: typeof undefined;

Undefined

null

undefined

None of the above

7.		Which of the following is a valid way to declare and initialize a number variable in JavaScript?

var myNum = 42;

let myNum = 3.14;

const myNum = -99;

All of the above

8.		Which of the following is not a valid way to declare and initialize a variable in JavaScript?

var myVar = 1;

myVar = 1;

let myVar = 1;

const myVar = 1;

9.		What is the data type of a variable that stores an undefined value in JavaScript?

Undefined

Null

Object

None of the above

10.		Which of the following is a valid way to declare and initialize an object with multiple properties in JavaScript?

var myObj = {key1: "value1", key2: "value2"};

let myObj = {"key1": "value1", "key2": "value2"};

const myObj = {key1: "value1", key2: "value2"};

All of the above