JavaScript快速入门（二）
文件中引入JavaScript嵌入到HTML文件中
在body或者head中添加script标签
引入js文件
创建一个js文件
var age = 20;
console.log(age);在html文件中src引入改文件
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</body>引入网络来源文件，和引入本地的js文件一样，通过src
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</body> 数据类型
原始数据类型：基本的数据类型（数值、字符串、布尔值）
复合数据类型：对象（一个对象可以看做是存放各种值得容器，由基础数据类型组成）
var user = {<body>
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</body>"name":"ming",<body>
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</body>age:20,<body>
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</body>is_register:True} 特殊数据类型：null和undefined
typeof可以用来判断基础数据类型
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</body>算数运算符
加减乘除取余：+ 、-、*、/、%
自增或者自减相当于当前值+1或者-1
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</body>自增自减需要注意，有两种写法一种运算符号在前，一种运算符号在后，两种效果不一样
运算符号在前是先自增再运行，运算符号在后是先运行在自增
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</body> 赋值运算符
赋值运算符表达式=赋值运算符+=x +=y 等同于 x= x+y-=x -=y 等同于 x = x-y*=x *= y 等同于 x = x*y/=x /= y 等同于 x = x/y%=x %= y 等同于 x = x % y比较运算符
比较运算符描述</tdtd小于/td/trtrtd>大于=大于或者等于==相等===严格相等!=不相等!==严格不相等== 和 ===区别
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</body>布尔运算符
取反运算符（！）
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</body>提示 undefind 、null、false、0、NaN、空字符串 取反都为true
且运算符（&&）
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</body>活运算符（||）
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</body> 用Switch简化多个if...else....
swith后面跟表达式，case后面记得一定要加上break，不加上break会把后续的都执行，最后default就是以上case都不是执行
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</body> 用三目运算符来代替if...else...
？y ：x
表达式正确返回y，错误则返回x
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</body> 字符串
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</body>用属性length来查看字符串长度
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</body>charAT查看索引位置的字符串
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</body>concat连接两个字符串，创建新的字符串，不影响老的字符串（拼接的如果不是字符串，也会先转为str再拼接）
同样也可以用“+”拼接
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</body>concat和+号的区别
+号会先运算数字类型在转，所以下方会先做1+2后再转字符串
concat不管什么，都会转字符串拼接
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</body>substring截取字符串，两个参数，参数1开始的位置的索引，第二个参数结束位置的索引（结束索引位置不取，左闭右开）
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</body>substr用法基本和substring一样，区别是第二个参数不在是结束位置的索引，而是字符串的长度
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</body>indexof查询字符串第一次出现的位置，不存在则返回-1
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</body>trim方法去除首尾两端的空格，包括\r \n \t都能去掉
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</body>split方法是按分隔符，返回一个分割出来的字符串数组
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</body> 数组
查询、追加
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</body>遍历
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</body>数组静态方法Array.isArray()：判断是否为数组
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</body>push()/pop()方法：改变原数组末尾增加或删除
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</body>shift()/unshift：改变原数组在数组起始位置添加或删除
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</body>join按指定分隔符拼接数组成员，默认都是逗号
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</body>concat数组合并
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</body>reverse翻转
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</body>indexof返回元素在数组中第一次出现的位置，没有则返回-1
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来源:https://www.cnblogs.com/yetangjian/p/17253215.html
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