Getting started with JavaScript variables

This article mainly introduces the Getting Started Tutorial on understanding JavaScript variables. it is the basic knowledge in JS getting started. if you need it, you can refer to the following variable as a container for storing information:

x=5; length=66.10;

Do you still remember the algebra I learned at school?

When you recall the algebra courses you have learned at school, you may think of x = 5, y = 6, z = x + y, and so on.

Remember, a letter can save a value (for example, 5), and the above information can be used to calculate that the value of z is 11.

You must have forgotten it, right.

These letters are called variables and can be used to save values (x = 5) or expressions (z = x + y ).

JavaScript variables

Like algebra, JavaScript variables are used to save values or expressions.

You can give the variable a brief name, such as x or a descriptive name, such as length.

JavaScript variables can also save text values, such as carname = "Volvo ".

Rules for JavaScript variable names:

Variables are case sensitive (y and Y are two different variables)

The variable must start with a letter or underscore

Note: JavaScript is case sensitive and variable names are also case sensitive.

Instance

You can change the value of a variable during script execution. You can reference a variable by its name to display or change its value.

This example shows how it works.

Declare (create) JavaScript variables

Variable creation in JavaScript is often called a "declaration" variable.

You can declare JavaScript variables using the var statement:

var x;var carname;

After the preceding declaration, variables have no values, but you can assign values to them when declaring them:

var x=5;var carname="Volvo";

Note: when assigning a text value to a variable, enclose the value with quotation marks.

Assign values to JavaScript variables

Assign values to JavaScript variables using the assignment statement:

x=5;carname="Volvo";

The variable name is on the left of the = symbol, and the value to be assigned to the variable is on the right of the = symbol.

After the preceding statement is executed, the value saved in variable x is 5, and the carname value is Volvo.
Assign values to undeclared JavaScript variables

If the variable you assign has not been declared, the variable is automatically declared.

These statements:

x=5;carname="Volvo";

The effects of these statements are the same:

var x=5;var carname="Volvo";

Redeclare JavaScript variables

If you declare a JavaScript variable again, the variable will not lose its original value.

var x=5;var x;

After the preceding statement is executed, the value of variable x is still 5. When the variable is declared again, the value of x is not reset or cleared.

JavaScript arithmetic

Like algebra, you can use JavaScript variables for arithmetic:

y=x-5;z=y+5;