The meaning of javascript variables

Variables in JavaScript are "containers" used to store information; JavaScript variables can be used to store values ​​and expressions; JavaScript variables can also store other data types, such as text values.

The operating environment of this article: windows7 system, javascript version 1.8.5, Dell G3 computer.

The meaning of javascript variables

Variables are "containers" used to store information.

Example

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 (like x) to hold values ​​(like 5).

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

In JavaScript, these letters are called variables.

lamp You can think of variables as containers for storing 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 more descriptive names (such as age, sum, totalvolume).

• Variables must start with a letter

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

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

lamp JavaScript statements and JavaScript variables are both case-sensitive.

JavaScript Data Types

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

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

JavaScript variables come in many types, but for now, we’ll just focus on numbers and strings.

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

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

Example

var pi=3.14;  
// 如果你熟悉 ES6，pi 可以使用 const 关键字，表示一个常量
// const pi = 3.14;
var person="John Doe";
var answer='Yes I am!';

Declaring (Creating) JavaScript Variables

Creating a variable in JavaScript is often called "declaring" a variable.

We use the var keyword to declare a variable:

var carname;

After a 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 also assign a value to a variable when you declare it:

var carname="Volvo";

In the following example, We create a variable named carname, assign it the value "Volvo", and then put it into the HTML paragraph with id="demo":

Example

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

[Related recommendations: javascript advanced tutorial】

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