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Variable names

Variable names must conform to the naming rules for identifiers. A JavaScript identifier must start with a letter or underscore "_". Following this, you can use either letters or the symbols for the digits (0-9)in the variable name.

JavaScript is case sensitive. Therefore letters include the characters "A" through "Z" (uppercase) and the characters "a" through "z" (lowercase).

Declaring a variable

In many languages, including JavaScript, you must declare a variable before you can use it. However, JavaScript is very loose in this regard. There are two ways to declare a variable in JavaScript:

  • By simply assigning it a value; for example, x = 10
  • By using the keyword var ; for example, var x = 10

Scope

When working with variables in JavaScript and other languages as well, you must always be concerned about an issue known as scope. Among other things, scope determines which statements in a script have access to a variable.

Two kinds of variables

JavaScript recognizes two kinds of variables:

  • local
  • global

Local variables are variables that are declared inside a function. Global variables are variables that are declared outside a function.

Scope

Local variables may only be accessed by other code within the same function following the declaration of the variable. Hence, the scope of local variables is limited to the function or method inwhich it is declared.

Global variables may be accessed by any code within the script following the declaration of the variable. Hence, the scope of global variables is the entire script.

Use of the keyword var

Using var to declare a global variable is optional. However, you must use var to declare a variable inside a function (a local variable).

A sample script that uses variables

A sample script that uses variables to store data is shown in Listing 4 .

Listing 4 . A sample script that uses variables.
<!-- File JavaScript04.html --><html><body><script language="JavaScript1.3">//Define the function named getArea() function getArea(theRadius) {//declare a local variable var theArea//calculate the area theArea = Math.PI * theRadius * theRadiusreturn theArea }//end function getArea()//=========================================// //declare a global variable without keyword vararea = getArea(3.2)//call the function document.write("Area is: " + area)</script></body></html>

The area of a circle

Listing 4 begins by defining a function that will compute and return the area of a circle given the radius of the circle as an incoming parameter.

The code in the function begins by declaring a variable named theArea . Effectively, this declaration sets aside a pigeon hole in memory and gives it the name theArea . Once the variable is declared, it can be accessed by calling out its name. It can be used to store data, or it can be used to retrievedata previously stored there.

Behavior of the function named getArea

You may recall that the area of a circle is calculated by multiplying the mathematical constant PI by the radius squared. There is no squaringoperator in JavaScript. Therefore, you can square a value by multiplying it by itself.

Questions & Answers

show that the set of all natural number form semi group under the composition of addition
Nikhil Reply
explain and give four Example hyperbolic function
Lukman Reply
_3_2_1
felecia
⅗ ⅔½
felecia
_½+⅔-¾
felecia
The denominator of a certain fraction is 9 more than the numerator. If 6 is added to both terms of the fraction, the value of the fraction becomes 2/3. Find the original fraction. 2. The sum of the least and greatest of 3 consecutive integers is 60. What are the valu
SABAL Reply
1. x + 6 2 -------------- = _ x + 9 + 6 3 x + 6 3 ----------- x -- (cross multiply) x + 15 2 3(x + 6) = 2(x + 15) 3x + 18 = 2x + 30 (-2x from both) x + 18 = 30 (-18 from both) x = 12 Test: 12 + 6 18 2 -------------- = --- = --- 12 + 9 + 6 27 3
Pawel
2. (x) + (x + 2) = 60 2x + 2 = 60 2x = 58 x = 29 29, 30, & 31
Pawel
ok
Ifeanyi
on number 2 question How did you got 2x +2
Ifeanyi
combine like terms. x + x + 2 is same as 2x + 2
Pawel
x*x=2
felecia
2+2x=
felecia
Mark and Don are planning to sell each of their marble collections at a garage sale. If Don has 1 more than 3 times the number of marbles Mark has, how many does each boy have to sell if the total number of marbles is 113?
mariel Reply
Mark = x,. Don = 3x + 1 x + 3x + 1 = 113 4x = 112, x = 28 Mark = 28, Don = 85, 28 + 85 = 113
Pawel
how do I set up the problem?
Harshika Reply
what is a solution set?
Harshika
find the subring of gaussian integers?
Rofiqul
hello, I am happy to help!
Shirley Reply
please can go further on polynomials quadratic
Abdullahi
hi mam
Mark
I need quadratic equation link to Alpa Beta
Abdullahi Reply
find the value of 2x=32
Felix Reply
divide by 2 on each side of the equal sign to solve for x
corri
X=16
Michael
Want to review on complex number 1.What are complex number 2.How to solve complex number problems.
Beyan
yes i wantt to review
Mark
use the y -intercept and slope to sketch the graph of the equation y=6x
Only Reply
how do we prove the quadratic formular
Seidu Reply
please help me prove quadratic formula
Darius
hello, if you have a question about Algebra 2. I may be able to help. I am an Algebra 2 Teacher
Shirley Reply
thank you help me with how to prove the quadratic equation
Seidu
may God blessed u for that. Please I want u to help me in sets.
Opoku
what is math number
Tric Reply
4
Trista
x-2y+3z=-3 2x-y+z=7 -x+3y-z=6
Sidiki Reply
can you teacch how to solve that🙏
Mark
Solve for the first variable in one of the equations, then substitute the result into the other equation. Point For: (6111,4111,−411)(6111,4111,-411) Equation Form: x=6111,y=4111,z=−411x=6111,y=4111,z=-411
Brenna
(61/11,41/11,−4/11)
Brenna
x=61/11 y=41/11 z=−4/11 x=61/11 y=41/11 z=-4/11
Brenna
Need help solving this problem (2/7)^-2
Simone Reply
x+2y-z=7
Sidiki
what is the coefficient of -4×
Mehri Reply
-1
Shedrak
A soccer field is a rectangle 130 meters wide and 110 meters long. The coach asks players to run from one corner to the other corner diagonally across. What is that distance, to the nearest tenths place.
Kimberly Reply
Jeannette has $5 and $10 bills in her wallet. The number of fives is three more than six times the number of tens. Let t represent the number of tens. Write an expression for the number of fives.
August Reply
What is the expressiin for seven less than four times the number of nickels
Leonardo Reply
How do i figure this problem out.
how do you translate this in Algebraic Expressions
linda Reply
why surface tension is zero at critical temperature
Shanjida
I think if critical temperature denote high temperature then a liquid stats boils that time the water stats to evaporate so some moles of h2o to up and due to high temp the bonding break they have low density so it can be a reason
s.
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
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Source:  OpenStax, Accessible physics concepts for blind students. OpenStax CNX. Oct 02, 2015 Download for free at https://legacy.cnx.org/content/col11294/1.36
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