[JavaScript tutorial] JavaScript Variables

A variable is a & quot; Container & quot; used to store information ;.

JavaScript Variables

A variable is a "Container" used to store information ".

Instance

var x=5;var y=6;var z=x+y;

Just like Algebra

X = 5
Y = 6
Z = x + y

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

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

In JavaScript, these letters are called variables.

You can think of variables as containers that store data.

JavaScript Variables

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

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

The variable must start with a letter.

Variables can also start with $ and _ (but we do not recommend this)

Variable names are case sensitive (y and Y are different variables)

Both JavaScript statements and JavaScript variables are case sensitive.

JavaScript Data Type

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

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

JavaScript variables have many types, but now we only focus on numbers and strings.

When you assign a text value to a variable, it should be enclosed by double quotation marks or single quotation marks.

Do not use quotation marks when you assign a value to the variable. If you enclose a value in quotation marks, the value is processed as text.

Instance

var pi=3.14;var person="John Doe";var answer='Yes I am!';

Declare (create) JavaScript Variables

Creating a variable in JavaScript is usually called a "Declaration" variable.

We use the var keyword to declare the variable:

var carname;

After the variable is declared, the variable is empty (it has no value ).

To assign a value to a variable, use the equal sign:

carname="Volvo";

However, you can assign values to variables when declaring them:

var carname="Volvo";

In the following example, a variable named carname is created and assigned "Volvo" to it, which is then included in the HTML section of id = "demo:

Instance

var carname="Volvo";document.getElementById("demo").innerHTML=carname;

A good programming habit is to declare the required variables at the beginning of the Code.

One statement and multiple variables

You can declare many variables in a statement. This statement starts with var and uses commas to separate variables:

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

The statement can also span multiple rows:

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

Value = undefined

Variables without values are often declared in computer programs. A variable declared without a value. Its value is actually undefined.

After the following statement is executed, the carname value of the variable is undefined:

var carname;

Redeclare JavaScript Variables

If you declare a JavaScript variable again, the value of the variable will not be lost:

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

var carname="Volvo"; var carname;

JavaScript count

You can use JavaScript variables to calculate the number. The = and + operators are used:

Instance

y=5;x=y+2;

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

The above is the content of the JavaScript variable in the [JavaScript tutorial]. For more information, see the PHP Chinese website (www.php1.cn )!