what is a variable in js

JavaScript variables are used to store information, declared through the var, let or const keywords, and assigned values ​​using the assignment operator (=). They can accommodate various types such as strings, numbers, and Boolean values. value. Among them, variables declared by var belong to the global scope, variables declared by let belong to the block scope, and constant variables declared by const cannot be changed.

What are JavaScript variables?

In JavaScript, a variable is used to store information. It is a named reference that is assigned a value. Variables can be declared using the var, let or const keywords and can be assigned a value using the assignment operator (=).

Variable Type

JavaScript variables can hold various types of values, including:

• String: A sequence of text enclosed in quotes (") or single quotes (').
• Number: Integer or floating point number.
• Boolean value: True or false.
• undefined: Indicates an undefined value.
• ##null: Explicitly indicates no value.
• Object: A complex data structure containing properties and methods
• Array: An ordered collection of values. #Variable declaration

Use var, let or const to declare variables:

var:

Allows variables to be declared within the function scope, all The declared variables belong to the global scope.

• ##let: Allows variables to be declared in the block scope and is only available within the declared block.
##const:
• Allows the declaration of constant variables, whose values ​​cannot be changed after declaration.
• Variable assignment
Use the assignment operator (=) to assign variables. Value:

<code class="javascript">let name = "John";
const age = 30;</code>

Variables use

to access declared variables through variable names:

<code class="javascript">console.log(name); // 输出："John"</code>

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