Type of Operator:
The type of operator is used to get the data type (returns a string) of its operand. The operand can be either a literal or a data structure such as a variable, a function, or an object. The operator returns the data type.
Syntax:
typeof operand or type of(operand)
typeof returns: boolean, function, number, strinq, and undefined. The following table summarizes possible values returned by the type of operator.

Write statement general syntax:
document write ("string" + var);
Ex: document write ("The Sum of Data1 and Data2 : "+sum);

Variable is a memory location where value can be stored. Variable is a symbolic name for a value. Variables are declared with the var keyword in JavaScript. Every variable has a name, called identifier.
Ex: var nl = 522; Here nl is a variable. 522 is a value stored on it.

JavaScript supports three important types of dialog boxes. Dialog boxes are also called as Popup Boxes These dialog boxes can be used to raise an alert, or to get confirmation on any input or to have a kind of input from the users.

There are three types of expressions as follows,
(i) Arithmetic expressions
(ii) Relational expressions
(iii) Logical expressions

An expression is a phrase of JavaScript that a JavaScript interpreter can evaluate to produce a value. The data types are used directly as literals or within variables in combination with simple operators, such as addition, subtraction, and so on, to create an expressions.

Variable is a memory location where value can be stored. Variable is a symbolic name for a value Variables are declared with the var keyword in JavaScript. Every variable has a name, called identifier.

The Lexical structure specifies variable names, the delimiter characters for comments, and how one program statement is separated from the next.

It provides a common scripting language for Web developers to design, test and deploy Internet Applications.

There are two types of comments, Single line and Multiple line comments. Single-line comments begin with a double slash (//), causing the interpreter to ignore everything from that point to the end of the line. Multiple line comments begins with /* and ends with */.

The?: is the conditional operator in JavaScript, which requires three operands, hence it is called the ternary operator. The syntax is
var variablename=(condition) ?value 1: value2;
Example :var result=(10>15)?100 :150;

There are 5 type of literals in JavaScript. They are Integer, Floating Point, Character, String and Boolean.

Type casting is the act of converting one data type into a different data type which is also called as casting. In JavaScript there are two type of casting,
(i) Implicit casting and
(ii) Explicit casting
Implicit casting occurs automatically in JavaScript when you change the data stored in a variable:

The scope of a variable is the life time of a variable of source code in which it is defined.
A global variable has global scope; it can be defined everywhere in the JavaScript code.
Variables declared within a function are defined only within the body of the function. They are local variables and have local scope.