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Variables in JavaScript: Declaration, Initialization, and Scope

Rumman Ansari July 09, 2024 9,152 views

A JavaScript variable is simply a name of storage location. There are two types of variables in JavaScript : local variable and global variable.

There are some rules while declaring a JavaScript variable (also known as identifiers).

Variables are the identifiers to store data values in our code.
var is the keyword to declare a variable.
‘=’ is the operator to assign a value to a variable.
A variable must start with _ or $ or letter. 99temp is invalid whereas _99temp is valid.
In ES2015(known as ECMAscript), two other ways to declare variables were introduced- let and const. We can use these 2 keywords to define variables(now recommended).

Correct JavaScript variables


var x = 10;  
var _value="hello";

Incorrect JavaScript variables


var  123=310;  
var *bb=340;

In later chapter we will discuss about local and global variable.

Solve these below questions.

Sample Question 1:

Declare two variables with values such as "Tom", "Jerry".
Concatenate these strings.
Print the result in a way that the output is "Tom and Jerry".

Sample Question 2:

Assigning two strings with values "This is", "JavaScript".
Concatenate these strings.
Find out the length of the resultant string using ".length".

Sample Question 3:

Print the date as 01-Jan-2016 when

var year = 2016
var month = Jan
var date = 1

Sample Question 4:

Write JavaScript program to convert ?C (Celsius) to ?F (Fahrenheit). You can prompt the user for input ?C using window.prompt. Formula for converting ?C to ?F is

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