SRC attribute <html> <head> <title> SRC attribute of the script tag </title> </head> <body> <script language="Java Script"src=src. js><! ></script> </body> </html>
SRC attribute <html> <head> <title>SRC attribute of the script tag.</title> </head> <body> <script language="JavaScript" src="src.js"><!-- --></script> </body> </html>
Hi Web surfers V arable definition Welcome to Mastering Java Script and Script <html> <head> <title> Using Java Script to ceate HTML tags</title> <script language="JavaScript > greeting="<h1>Hi Web surfers! </h1>i welcome="<p>Welcome to <em> Mastering JavaScript and JScript </em>.</p>" --></script> </head> <body> <script language=" Javascript >< document. write(greeting); document. write (welcome) ></script> </ body> </html>
Variable definition <html> <head> <title>Using JavaScript to ceate HTML tags</title> <script language="JavaScript"><!-- greeting="<h1>Hi Web surfers!</h1>"; welcome="<p>Welcome to <em>Mastering JavaScript and JScript</em>.</p>"; --></script> </head> <body> <script language="JavaScript"><!-- document.write(greeting); document.write(welcome); --></script> </body> </html>
变量 口变量名区别字母大小写 口变量不要求指定其数据类型,由赋值的数据类型 确定 口美元符号($)是保留字,不可用于变量命名
变量 变量名区别字母大小写 变量不要求指定其数据类型，由赋值的数据类型 确定 美元符号（$）是保留字，不可用于变量命名
数据类型 数据类型 说明 举例 Number整数、浮点数和NaN 19,0×13,023,1e-2 Boolean逻辑值tue(1)和lse(0)True, false String 单引号或双引号中的字符串 JavaScript and ]Script Hello World! Null 定义空或不存在引用 设置成相应类型的默认值 Undefined变量还未赋值 设置成相应类型的默认值
数据类型 Undefined 变量还未赋值 设置成相应类型的默认值 Null 定义空或不存在引用 设置成相应类型的默认值 "JavaScript and JScript", 'Hello World!' String 单引号或双引号中的字符串 Boolean 逻辑值true(1)和false(0) True, false Number 整数、浮点数和NaN 19, 0x13, 023, 1e−2 数据类型 说明 举例
Null and undefined a(null = undefined) is true a(null == undefined )is false a(typeof null)is object n(typeof undefined) is undefined
Null and Undefined (null == undefined) is true (null === undefined) is false (typeof null) is object (typeof undefined) is undefined