JavaScript Basics Variables

1. Variable Overview

1.1 Storage of variables in memory

Essence: A variable is a piece of space in memory that a program applies for to store data.

1.2 Use of variables

The use of variables is divided into two steps: 1. Declare variables 2. Assign values

1. Declare variables

//Declare a variable named age

var is a JS keyword used to declare a variable. After declaring a variable using this keyword, the computer will automatically allocate memory space for the variable. age is the name of the defined variable. We need to access the allocated space in the memory through the variable name.

2. Assignment

age = 10; //Assign the value of age variable to 10

3. Initialization of variables

var age = 10;

1.3 Variable Syntax Extension

1. Update variables

When a variable is reassigned, its original value will be overwritten and the variable value will be based on the last assigned value.

2. Declare multiple variables

When declaring multiple variables at the same time, just write one var, and separate multiple variable names with commas.

var age = 10,name = 'lili',sex = 2;

3. Special cases for declaring variables

1.5 Variable Naming Conventions

• It is composed of letters (AZ az), numbers (0-9), underscores (_), and dollar signs ($), such as: usrAge, num01, _name
• Strictly distinguish between uppercase and lowercase letters. var APP; and var app; are two variables.
• Cannot start with a number
• It cannot be a keyword or a reserved word, such as for, var, while
• Variable names must be meaningful
• Follow camelCase naming convention. The first letter is lowercase, and the first letter of the following words is capitalized. myFirstName
• Recommended translation website: Youdao iCiBa

Summarize

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