Is this valid JavaScript code?

Tip: JavaScript is a loosely typed language

Answer: Yes.

Explanation: JavaScript is a loosely typed language, as opposed to strongly typed languages like Java. JavaScript variables have no predetermined type. Instead, the type of a variable is the type of its value. So you can assign value of any type to the variable.

var x; // typeof x is undefined
x = "Hello"; // typeof x is String 
x=[1,2,3]; // typeof x is Object 
x=5; // typeof x is Number

int x; // x is declared to hold integer numbers only
x = 10; // valid statement
x= "Hello"; // Error! It is not allowed assign String to int variable