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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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