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JavaScript Variables


JavaScript variables

Like algebra, JavaScript variables can be used to hold values (such as x = 5) and expressions (such as z = x + y).

Variables can use short names (such as x and y) or more descriptive names (such as age, sum, totalvolume).

  • Variable must start with a letter
  • Variables can also start with $ and _ symbols (though we don't recommend this)
  • Variable names are case sensitive (y and Y are different variables)
Both JavaScript statements and JavaScript variables are case sensitive.

Like algebra

x = 5
y = 6
z = x + y

In algebra, we use letters (such as x) to hold values (such as 5).

With the expression z = x + y above, we can calculate the value of z as 11.

In JavaScript, these letters are called variables.

note: Think of variables as containers for storing data.

Much Like Algebra

In this precedent, item1, item2, and complete, are variables:

Example

var item1 = 8;
var item2 = 7;
var all out = itme1 + item2;
Try it Yourself »

In programming, much the same as in polynomial math, we use factors (like price1) to hold values.

In programming, much the same as in polynomial math, we use factors in articulations (complete = price1 + price2).

From the precedent above, you can ascertain the aggregate to be 11.

JavaScript Identifiers

All JavaScript variables must be identified with unique names.

These remarkable names are called identifiers.

Identifiers can be short names (like x and y), or increasingly graphic names (age, entirety, totalVolume).

The general principles for building names for factors (remarkable identifiers) are:

  • Names can contain letters, digits, underscores, and dollar signs.
  • Names must start with a letter
  • Names can likewise start with $ and _ (however we won't utilize it in this tutorial)
  • Names are case delicate (y and Y are distinctive variables)
  • Reserved words (like JavaScript watchwords) can't be utilized as names

The Assignment Operator

In JavaScript, the equivalent sign (=) is a "assignment" administrator, not an "equal to" operator.

This is not the same as variable based math. The accompanying does not bode well in algebra:

x = x + 8

In JavaScript, be that as it may, it bodes well: it relegates the estimation of x + 8 to x.


JavaScript Data Types

JavaScript variables can also hold other data types, such as text values (name = "Bill Gates").

In JavaScript, a piece of text like "Bill Gates" is called a string.

There are many types of JavaScript variables, but for now, we are only concerned with numbers and strings.

When you assign a text value to a variable, you should enclose the value in double or single quotes.

Do not use quotes when the value you assign to a variable is numeric. If you surround the value with quotes, the value is treated as text.

Example

var pi = 3.14;
var individual = "Sophie";
var answer = 'Yes I am!';
Try it Yourself »

One statement, multiple variables

You can declare many variables in one statement. The statement starts with var and the variables are separated by commas:

var lastname = "Doe", age = 30, job = "carpenter";

Declarations can alsospan multiple lines:

var lastname = "Doe",
age = 30,
job = "carpenter";

Multiple declarations in a statement cannot be assigned the same value:

var x, y, z = 1;

x, y is undefined and z is 1.



Value = undefined

In computer programs, variables with no value are often declared. A variable declared without a value is actually undefined.

After executing the following statement, the value of the variable carname will be undefined:

var carname;


Redeclaring JavaScript variables

If you redeclare a JavaScript variable, its value will not be lost:

After the following two statements are executed, the value of the variable carname is still "Volvo":

var carname = "Volvo";
var carname;


JavaScript arithmetic

You can do arithmetic with JavaScript variables, using operators such as = and +:

Example

y = 5 ; x = y + 2 ;

You will learn more about JavaScript operators later in this tutorial.