Can there be spaces in JavaScript variables?

In JavaScript, variable names cannot have spaces, but variable values ​​can have spaces. The variable name can contain numbers, letters, underscores and dollar signs, but Chinese characters and spaces cannot appear; and the variable value can have spaces, just define the variable value as a string type, for example "var a="hello world";" .

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

JavaScript variable names cannot have spaces, but variable values ​​can have spaces.

JavaScript variable names

In JavaScript, variable names cannot be defined casually and need to follow the naming rules of identifiers, as shown below :

• ##The variable name can contain numbers, letters, underscores

  _, dollar signs $;

• Chinese characters cannot appear in the variable name;

• The variable name cannot contain spaces;

• The variable name cannot be a keyword in JavaScript , reserved words;

• The variable name cannot start with a number, that is, the first character cannot be a number.

JavaScript Keywordsbreakdelete ifthis whilecasedointhrowwith catch else instanceof trycontinue finally new typeofdebugger（ECMAScript 5 new）for return vardefault function switch void##JavaScript reserved wordsabstract ##boolean enum implements package superbyte export import private synchronizedchar extends int protected throwsfinal float In definition When using variables, the variable name should be as meaningful as possible so that you or others can easily understand it. For example, you can use name to define a variable that stores names, and use dataArr to define an array type variable.

double	goto	native	static
				##class
interface	public	transient		const
long	short	volatile

When the variable name contains multiple English words, it is recommended to use camel case naming (big camel case: the first letter of each word is capitalized, such as FileType, DataArr; small camel case: the first letter of the word Capitalize the first letter of the words after lowercase, such as fileType, dataArr).

JavaScript variable value

After the variable is defined, you can use the equal sign = to assign a value to the variable, the equal sign The left side is the name of the variable, and the right side of the equal sign is the value to be assigned to the variable, as shown in the following example:

var num;    // 定义一个变量 num
num = 1;    // 将变量 num 赋值为 1

JavaScript is a dynamically typed language. When defining a variable, you do not need to specify the variable type in advance. The type of the variable is dynamically determined by the JavaScript engine during the running of the program. In addition, you can use the same variable to store different types of data, for example: <pre class="brush:php;toolbar:false">var a; // 此时 a 为 Undefined a = &quot;http://c.biancheng.net/&quot;; // 此时 a 为 String 类型 a = 123; // 此时 a 为 Number 类型</pre>The data types in JavaScript can be divided into two types Type:

Basic data types (value types): String, Number, Boolean, Null, Undefined, Symbol ;

• Reference data type: Object, Array, Function.

• JavaScript string

The string (String) type is a piece of text wrapped in single quotes '' or double quotes "" , such as '123', "abc". It should be noted that single quotes and double quotes are different ways of defining a string and are not part of the string. When defining a string, if the string contains quotes, you can use backslash

\

to escape the quotes in the string, or choose different quotes from the string to define String, as shown in the following example:

var str = "Let's have a cup of coffee.";  // 双引号中包含单引号
var str = 'He said "Hello" and left.';    // 单引号中包含双引号
var str = 'We\'ll never give up.';        // 使用反斜杠转义字符串中的单引号

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