What are the requirements for naming variables in javascript

Requirements for variable naming in JavaScript: 1. Strictly case-sensitive; 2. Can only contain letters, numbers, and underscores, and spaces and other punctuation marks are not allowed; 3. Must start with a letter or underscore, and cannot Start with a number; 4. Keywords and reserved words cannot be used as variable names; 5. Try to avoid using meaningless names.

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

You can use keywords: const, var, let to define variables in javascript, syntax:

关键字 变量名;

Variables are equivalent to containers, values ​​are equivalent to what is contained in the container, and the variable name is the container The label attached to the variable allows you to find the variable so that you can read and write the value it stores.

Note: Variable names cannot be defined arbitrarily. A valid variable name should meet the following requirements:

• Variable name Case-sensitive

• Variable names can only contain letters (A~z), numbers (0~9) and underscores (_). Spaces and other punctuation marks are not allowed

• Variable names must start with letters or underscores, not numbers

• It is prohibited to use JavaScript keywords and reserved words as variable names

• The length of variable naming should be as short as possible, and the key points should be grasped, and the type of value should be reflected in the variable name as much as possible

• Try to avoid using meaningless naming

Common variable name naming methods include Hungarian nomenclature, camel case nomenclature and Pascal nomenclature

Hungarian nomenclature

Hungarian nomenclature Hungarian nomenclature is a variable naming rule in computer programming. This nomenclature can be subdivided into: system Hungarian nomenclature and Hungarian application nomenclature.

Hungarian nomenclature has language-independent characteristics and is widely used in BCPL language for the first time. Since BCPL has only one data type, machine words, the language itself cannot help programmers remember the types of variables. Hungarian nomenclature solves this problem by clarifying the data type of each variable.

In Hungarian nomenclature, a variable name begins with one or more lowercase letters that help remember the variable's type and purpose, followed by whatever name the programmer chooses. The first letter of this second half may be capitalized to distinguish it from the preceding type designator letter.

Syntax

变量名 = 类型 + 对象描述

• Type refers to the type of the variable

• Object description refers to the full name of the object or Part of the name must have a clear meaning, and the naming must be easy to remember and understand.

Indicate the type of the variable by adding the corresponding lowercase letter symbol in front of the variable name as a prefix. The prefix is ​​followed by one or more word combinations, and the words describe the purpose of the variable. If it is a jquery object, use $ as the prefix of the variable name.

Tips

Although javascript variables do not have types on the surface, javascript will still assign corresponding types to variables internally.

The Hungarian nomenclature was invented by a Microsoft programmer. Most c and c programs use this nomenclature.

Type

javascript variable naming type	Variable naming prefix
array array	a
boolean Boolean value	b
float floating point number	l
function function	fn
int integer	i
object object	o
regular regular	r
string string	s

示例

var aName = [1, 2, 3];
var oBtn = document.getElementById('btn');
function fnName(){};
var iCount = 0;
var sName = "zhuyujia";

驼峰式命名法

当变量名和函数名称是由二个或多个单字链接在一起，而构成的唯一识别字时，利用“驼峰式大小写”来表示，可以增加变量和函数的可读性。

“驼峰式大小写（Camel-Case）一词来自Perl语言中普遍使用的大小写混合格式，而Larry Wall等人所著的畅销书《Programming Perl》（O'Reilly出版）的封面图片正是一匹骆驼。”

“驼峰式大小写”命名规则可视为一种惯例，并无绝对与强制，为的是增加识别和可读性。一旦选用或设置好命名规则，在程序编写时应保持一致格式。

语法

变量名或函数名是由一个或多个单词连结在一起，其中第一个单词以小写字母开始，后面的所有单词的首字母都采用大写字母，这样的变量名看上去就像骆驼峰一样此起彼伏，故得名。

示例

var myName = "zhuyujia";
var formSubmit = document.getElementById("submit");
function timeCount(){}

帕斯卡命名法

Pascal命名法（Pascal Case，巴斯卡命名法／帕斯卡命名法），电脑程序编写时的一套命名规则（惯例）。

当变量名和函数名称是由二个或二个以上单字链接在一起，而构成的唯一识别字时，用以增加变量和函数的可读性。

单字之间不以空格断开或连接号（-）、下划线（_）链接，第一个单前缀字母采用大写字母；后续单字的首字母亦用大写字母，例如：FirstName、LastName。每一个单字的首字母都采用大写字母的命名格式，被称为“Pascal命名法”，源自于Pascal语言的命名惯例，也有人称之为“大驼峰式命名法”（Upper Camel Case），为驼峰式大小写的子集。

“Pascal命名法”可视为一种命名惯例，并无绝对与强制，为的是增加识别和可读性。一旦选用或设置好命名规则，在程序编写时应保持格式的一致性。

语法

和驼峰式命名法类似，只不过第一个单词的首字母需要大写。

示例

var myName = "zhuyujia";
var formSubmit = document.getElementById("submit");
function timeCount(){}

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