day29-JavaScript(1)
1、JavaScript 的历史1.1、JavaScript 的历史
JavaScript 因为互联网而生，紧随着浏览器的出现而问世。回顾它的历史，就要从浏览器的历史讲起。
1990年底，欧洲核能研究组织（CERN）科学家Tim Berners-Lee，在全世界最大的电脑网络——互联网的基础上，发明了万维网（World Wide Web），从此可以在网上浏览网页文件。最早的网页只能在操作系统的终端里浏览，也就是说只能使用命令行操作，网页都是在字符窗口中显示，这当然非常不方便。
1992年底，美国国家超级电脑应用中心（NCSA）开始开发一个独立的浏览器，叫做Mosaic。这是人类历史上第一个浏览器，从此网页可以在图形界面的窗口浏览。
1994年10月，NCSA的一个主要程序员Marc Andreessen联合风险投资家Jim Clark，成立了Mosaic通信公司（Mosaic Communications），不久后改名为Netscape。这家公司的方向，就是在Mosaic的基础上，开发面向普通用户的新一代的浏览器Netscape Navigator。
1994年12月，Navigator发布了1.0版，市场份额一举超过90%。
Netscape 公司很快发现，Navigator浏览器需要一种可以嵌入网页的脚本语言，用来控制浏览器行为。当时，网速很慢而且上网费很贵，有些操作不宜在服务器端完成。比如，如果用户忘记填写“用户名”，就点了“发送”按钮，到服务器再发现这一点就有点太晚了，最好能在用户发出数据之前，就告诉用户“请填写用户名”。这就需要在网页中嵌入小程序，让浏览器检查每一栏是否都填写了。
管理层对这种浏览器脚本语言的设想是：功能不需要太强，语法较为简单，容易学习和部署。那一年，正逢Sun公司的Java语言问世，市场推广活动非常成功。Netscape公司决定与Sun公司合作，浏览器支持嵌入Java小程序（后来称为Java applet）。但是，浏览器脚本语言是否就选用Java，则存在争论。后来，还是决定不使用Java，因为网页小程序不需要Java这么“重”的语法。但是，同时也决定脚本语言的语法要接近Java，并且可以支持Java程序。这些设想直接排除了使用现存语言，比如Perl、Python和TCL。
1995年，Netscape公司雇佣了程序员Brendan Eich开发这种网页脚本语言。Brendan Eich有很强的函数式编程背景，希望以Scheme语言（函数式语言鼻祖LISP语言的一种方言）为蓝本，实现这种新语言。
1995年5月，Brendan Eich只用了10天，就设计完成了这种语言的第一版。为了保持简单，这种脚本语言缺少一些关键的功能，比如块级作用域、模块、子类型（subtyping）等等，但是可以利用现有功能找出解决办法。这种功能的不足，直接导致了后来JavaScript的一个显著特点：对于其他语言，你需要学习语言的各种功能，而对于JavaScript，你常常需要学习各种解决问题的模式。而且由于来源多样，从一开始就注定，JavaScript的编程风格是函数式编程和面向对象编程的一种混合体。
Netscape 公司的这种浏览器脚本语言，最初名字叫做 Mocha，1995年9月改为LiveScript。12月，Netscape公司与Sun公司（Java语言的发明者和所有者）达成协议，后者允许将这种语言叫做JavaScript。这样一来，Netscape公司可以借助Java语言的声势，而Sun公司则将自己的影响力扩展到了浏览器。
之所以起这个名字，并不是因为JavaScript本身与Java语言有多么深的关系（事实上，两者关系并不深），而是因为Netscape公司已经决定，使用Java语言开发网络应用程序，JavaScript可以像胶水一样，将各个部分连接起来。当然，后来的历史是Java语言的浏览器插件失败了，JavaScript反而发扬光大。
1995年12月4日，Netscape 公司与 Sun 公司联合发布了 JavaScript 语言。当时的意图是将 JavaScript 作为 Java 的补充，用来操作网页。
1996年3月，Navigator 2.0 浏览器正式内置了 JavaScript 脚本语言。
1.2、JavaScript与ECMAScript的关系
1996年8月，微软模仿JavaScript开发了一种相近的语言，取名为JScript（JavaScript是Netscape的注册商标，微软不能用），首先内置于IE 3.0。Netscape公司面临丧失浏览器脚本语言的主导权的局面。
1996年11月，Netscape公司决定将JavaScript提交给国际标准化组织ECMA（European Computer Manufacturers Association），希望JavaScript能够成为国际标准，以此抵抗微软。ECMA的39号技术委员会（Technical Committee 39）负责制定和审核这个标准，成员由业内的大公司派出的工程师组成，目前共25个人。该委员会定期开会，所有的邮件讨论和会议记录，都是公开的。
1997年7月，ECMA组织发布262号标准文件（ECMA-262）的第一版，规定了浏览器脚本语言的标准，并将这种语言称为ECMAScript。这个版本就是ECMAScript 1.0版。之所以不叫JavaScript，一方面是由于商标的关系，Java是Sun公司的商标，根据一份授权协议，只有Netscape公司可以合法地使用JavaScript这个名字，且JavaScript已经被Netscape公司注册为商标，另一方面也是想体现这门语言的制定者是ECMA，不是Netscape，这样有利于保证这门语言的开放性和中立性。因此，ECMAScript和JavaScript的关系是，前者是后者的规格，后者是前者的一种实现。在日常场合，这两个词是可以互换的。
ECMAScript只用来标准化JavaScript这种语言的基本语法结构，与部署环境相关的标准都由其他标准规定，比如DOM的标准就是由W3C组织（World Wide Web Consortium）制定的。
一个完整的JavaScript包含三个部分：ECMAScript（标准语法），DOM以及BOM！
ECMA-262标准后来也被另一个国际标准化组织ISO（International Organization for Standardization）批准，标准号是ISO-16262。
1.3、JavaScript与Java的关系
JavaScript和Java是两种不一样的语言，但是它们之间存在联系。
JavaScript的基本语法和对象体系，是模仿Java而设计的。但是，JavaScript没有采用Java的静态类型。正是因为JavaScript与Java有很大的相似性，所以这门语言才从一开始的LiveScript改名为JavaScript。基本上，JavaScript这个名字的原意是“很像Java的脚本语言”。
在JavaScript语言中，函数是一种独立的数据类型，以及采用基于原型对象（prototype）的继承链。这是它与Java语法最大的两点区别。JavaScript语法要比Java自由得多。
另外，Java语言需要编译，而JavaScript语言则是运行时由解释器直接执行。
总之，JavaScript的原始设计目标是一种小型的、简单的动态语言，与Java有足够的相似性，使得使用者（尤其是Java程序员）可以快速上手。
1.4、JavaScript的版本
1997年7月，ECMAScript 1.0发布。
1998年6月，ECMAScript 2.0版发布。
1999年12月，ECMAScript 3.0版发布，成为JavaScript的通行标准，得到了广泛支持。
2007年10月，ECMAScript 4.0版草案发布，对3.0版做了大幅升级，预计次年8月发布正式版本。草案发布后，由于4.0版的目标过于激进，各方对于是否通过这个标准，发生了严重分歧。以Yahoo、Microsoft、Google为首的大公司，反对JavaScript的大幅升级，主张小幅改动；以JavaScript创造者Brendan Eich为首的Mozilla公司，则坚持当前的草案。
2008年7月，由于对于下一个版本应该包括哪些功能，各方分歧太大，争论过于激进，ECMA开会决定，中止ECMAScript 4.0的开发（即废除了这个版本），将其中涉及现有功能改善的一小部分，发布为ECMAScript 3.1，而将其他激进的设想扩大范围，放入以后的版本，由于会议的气氛，该版本的项目代号起名为Harmony（和谐）。会后不久，ECMAScript 3.1就改名为ECMAScript 5。
2009年12月，ECMAScript 5.0版正式发布。Harmony项目则一分为二，一些较为可行的设想定名为JavaScript.next继续开发，后来演变成ECMAScript 6；一些不是很成熟的设想，则被视为JavaScript.next.next，在更远的将来再考虑推出。TC39的总体考虑是，ECMAScript 5与ECMAScript 3基本保持兼容，较大的语法修正和新功能加入，将由JavaScript.next完成。当时，JavaScript.next指的是ECMAScript 6。第六版发布以后，将指ECMAScript 7。TC39预计，ECMAScript 5会在2013年的年中成为JavaScript开发的主流标准，并在此后五年中一直保持这个位置。
2011年6月，ECMAscript 5.1版发布，并且成为ISO国际标准（ISO/IEC 16262:2011）。到了2012年底，所有主要浏览器都支持ECMAScript 5.1版的全部功能。
2013年3月，ECMAScript 6草案冻结，不再添加新功能。新的功能设想将被放到ECMAScript 7。
2013年12月，ECMAScript 6草案发布。然后是12个月的讨论期，听取各方反馈。
2015年6月，ECMAScript 6正式发布，并且更名为“ECMAScript 2015”。这是因为TC39委员会计划，以后每年发布一个ECMAScirpt的版本，下一个版本在2016年发布，称为“ECMAScript 2016”。
除了ECMAScript的版本，很长一段时间中，Netscape公司（以及继承它的Mozilla基金会）在内部依然使用自己的版本号。这导致了JavaScript有自己不同于ECMAScript的版本号。1996年3月，Navigator 2.0内置了JavaScript 1.0。JavaScript 1.1版对应ECMAScript 1.0，但是直到JavaScript 1.4版才完全兼容ECMAScript 1.0。JavaScript 1.5版完全兼容ECMAScript 3.0。目前的JavaScript 1.8版完全兼容ECMAScript 5。
参考链接
2、JS的引入方式
1 直接编写
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};
2 导入文件
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};3、ECMAScript基本语法
js是一门弱类型的编程语言,属于基于对象和基于原型的脚本语言.
[*]变量
格式:
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};// 方式1 先声明再赋值
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var 变量名;var person = {
name: "alvin",
age: 18
}; // 声明的变量如果没有进行赋值,或者没有被定义的变量,值默认是undefined
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};变量名 = 变量值;
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};// 方式2 声明并赋值
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var 变量名 = 变量值;
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};// 方式3 一行可以声明多个变量.并且可以是不同类型
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var name="yuan", age=20, job="lecturer";1、声明变量时 可以不用var. 如果不用var 那么它是全局变量
2、变量命名,首字符只能是字母,下划线,$美元符 三选一，余下的字符可以是下划线、美元符号或任何字母或数字字符且区分大小写
[*]注释
// 单行注释
/*
var person = {
name: "alvin",
age: 18
}; 多行注释
*/
[*]语句分隔符
var a = 1var person = {
name: "alvin",
age: 18
}; // 分号和换行符作为语句分隔符号
var b = 2;
console.log(a,b)4、ECMAScript 基本数据类型
4.4.1、数字类型
JavaScript 没有整型和浮点型，只有一种数字类型，即number类型。
var x = 10;
var y = 3.14;
console.log(x,typeof x);var person = {
name: "alvin",
age: 18
};// 10 "number"
console.log(y,typeof y);var person = {
name: "alvin",
age: 18
};// 3.14 "number"4.4.2、字符串
字符串创建(两种方式)
[*]变量 = “字符串”
[*]字串对象名称 = new String (字符串)
var str1="hello world";
var str1= new String("hello word");// 字符串对象的操作
var str = "hello"; // 这就是字符串对象
console.log(str);
// 字符串对象内置属性
// length 计算字符串的长度
console.log( str.length );
// 字符串对象内置方法
// toUpperCase();var person = {
name: "alvin",
age: 18
};字母大写转换
// toLowerCase();var person = {
name: "alvin",
age: 18
};字母小写转换
console.log( str.toUpperCase() );
console.log( str.toLowerCase() );
// indexOf 获取指定字符在字符串中第一次出现的索引位置
// 字符串也有下标,也可以使用中括号来提取字符串的指定字符
console.log(str); // e
console.log( str.indexOf("e") ); // 1
// 切片,当前方法支持使用负数代表倒数下标
// slice(开始下标)var person = {
name: "alvin",
age: 18
}; 从开始位置切到最后
// slice(开始下标,结束下标)var person = {
name: "alvin",
age: 18
};从开始下标切到指定位置之前
var str = "helloworld";
var ret = str.slice(3,6); // 开区间,不包含结束下标的内容
console.log(ret); // low
var ret = str.slice(5);
console.log(ret); // world
var ret = str.slice(2,-1);
console.log(ret); // lloworl
var ret = str.slice(-4,-1);
console.log(ret); // orl
var ret = str.slice(-1,-4);
console.log(ret); // ""
// splitvar person = {
name: "alvin",
age: 18
}; 正则分割,经常用于把字符串转换成数组
var str = "广东-深圳-南山";
var ret = str.split("-");
console.log( ret );
// substrvar person = {
name: "alvin",
age: 18
};截取
var str = "hello world";
var ret = str.substr(0,3);
console.log(ret); // hel
// trimvar person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};移除字符串首尾空白
var password = "var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};ge llovar person = {
name: "alvin",
age: 18
}; ";
var ret = password.trim();
console.log(password.length); // 13
console.log(ret.length);var person = {
name: "alvin",
age: 18
};// 64.4.3、布尔值
1、Boolean类型仅有两个值：true和false，也代表1和0，实际运算中true=1,false=0
2、布尔值也可以看作on/off、yes/no、1/0对应true/false;
3、Boolean值主要用于JavaScript的控制语句
console.log(true);
console.log(false);
console.log(typeof true);
console.log(true === 1);
console.log(true == 1);
console.log(true + 1);
console.log(false + 1);4.4.4、空值（Undefined和Null）
[*]undefined类型
undefined类型只有一个值，即 undefined。
（1）当声明的变量未初始化时，该变量的默认值是 undefined。
（2）当函数无明确返回值时，返回的也是值 undefined;
[*]null类型
另一种只有一个值的类型是 null，它只有一个专用值 null，即它的字面量。值 undefined 实际上是从值 null 派生来的，因此 ECMAScript 把它们定义为相等的。
尽管这两个值相等，但它们的含义不同。undefined 是声明了变量但未对其初始化时赋予该变量的值，null 则用于表示尚未存在的对象。如果函数或方法要返回的是对象，那么找不到该对象时，返回的通常是 null。
4.4.5、类型转换
js中,类型转换有2种.一种就是强制转换,一种就是自动转换.
因为js是一门弱类型的脚本语言,所以变量会在运算符的运行要求,有时候根据运算符的要求,进行自动转换的.
[*]强制转换
// 1. 转换数据为数值类型
// parseIntvar person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
}; 把数据转换成整数
// parseFloatvar person = {
name: "alvin",
age: 18
}; 把数据转换成小数
// Numbervar person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
}; 把数据转换成数值
var box1 = "一共100件"; // 转换会失败
var box1 = "100件";var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
}; // 转换会成功
var ret = parseInt(box1);
console.log(box1);
console.log(ret);
//
var box2 = "3.14";
console.log(parseFloat(box2) ); // 3.14
//
var box3 = "3.14";var person = {
name: "alvin",
age: 18
}; // 使用Number转换的数据里面必须是纯数字!!!!否则都会转换失败
// var box3 = "3.1.4";var person = {
name: "alvin",
age: 18
};// 转换失败!
console.log( Number(box3) );
// 对于转换数值,如果转换失败的话,则结果为 NaN ,是 Not a Number ,但是NaN的类型也是number类型
// 2. 转换数据为字符串
// 变量.toString()
// String(数据)
var box4 = 3.14;
var ret = box4.toString();
console.log(ret);
//
ret = String(box4);
console.log(ret);
// 3. 转换数据成布尔类型
// Boolean()
var box5 = "";
console.log( Boolean(box5) ); // false
var box6 = -1;
console.log( Boolean(box6) ); // true
var box7 = 0;
console.log( Boolean(box7) ); // false;
var box8 = "false";
console.log( Boolean(box8) ); // true
var box9 = [];
console.log( Boolean(box9) ); // true
var box10 = {};
console.log( Boolean(box10) ); // true
var box11 = "0";
console.log( Boolean(box11) ); // true
var box12 = null;
console.log( Boolean(box12) ); // false
var box13 = undefined;
console.log( Boolean(box13) ); // false
[*]自动转换
// 所谓的自动转换,其实弱类型中的变量会根据当前代码的需要,进行类型的自动隐式转化
var box1 = 1 + true;
// true 转换成数值,是1, false转换成数值,是0
console.log(box1); // 2
var box2 = 1 + "200";
console.log(box2); // 1200 原因是,程序中+的含义有2种,第一: 两边数值相加, 第二: 两边字符串拼接.但是在js中运算符的优先级中, 字符串拼接的优先级要高于数值的加减乘除,所以解析器优先使用了+号作为了字符串的拼接符号了,因为程序就需要+号两边都是字符串才能完成运算操作,因此1变成字符串最终的结果就是 "1" +"200"
var box3 = 1 - "200";
console.log(box3); // -199;因为-号中表示的就是左边的数值减去右边的数值,因此程序就会要求"200"是数值,因此内部偷偷的转换了一下4.4.6、原始值和引用值
根据数据类型不同，有的变量储存在栈中，有的储存在堆中。具体区别如下：
原始变量及他们的值储存在栈中，当把一个原始变量传递给另一个原始变量时，是把一个栈房间的东西复制到另一个栈房间，且这两个原始变量互不影响。
引用值是把 引用变量的名称储存在栈中，但是把其实际对象储存在堆中，且存在一个指针由变量名指向储存在堆中的实际对象，当把引用对象传递给另一个变量时，复制的其实是指向实际对象的指针， 此时 两者指向的 是同一个数据，若通过方法改变其中一个变量的值，则访问另一个变量时，其值也会随之加以改变；但若不是通过方法 而是通过 重新赋值 此时 相当于 重新开了一个房间 该值的原指针改变 ，则另外一个 值不会随他的改变而改变。
// 初始值类型
var a = "yuan";
var b = a;
a = "alvin";
console.log(a);//alvin
console.log(b);//yuan
// 对象类型
var arr1=;
arr2 = arr1;
arr1.push(3);
console.log(arr1)//
console.log(arr2);//
arr1=;
console.log(arr1);//
console.log(arr2);//5、运算符
[*]运算符
/*
//算术运算符
var person = {
name: "alvin",
age: 18
}; +var person = {
name: "alvin",
age: 18
}; 数值相加
var person = {
name: "alvin",
age: 18
}; -var person = {
name: "alvin",
age: 18
}; 数值相减
var person = {
name: "alvin",
age: 18
}; *var person = {
name: "alvin",
age: 18
}; 数值相乘
var person = {
name: "alvin",
age: 18
}; /var person = {
name: "alvin",
age: 18
}; 数值相除
var person = {
name: "alvin",
age: 18
}; %var person = {
name: "alvin",
age: 18
}; 数值求余
var person = {
name: "alvin",
age: 18
}; **var person = {
name: "alvin",
age: 18
};数值求幂
var person = {
name: "alvin",
age: 18
}; a++ 数值后自增1var person = {
name: "alvin",
age: 18
}; a=a+1
var person = {
name: "alvin",
age: 18
}; ++a 数值前自增1var person = {
name: "alvin",
age: 18
}; a=a+1
var person = {
name: "alvin",
age: 18
}; b-- 数值后自减1var person = {
name: "alvin",
age: 18
}; b=b-1
var person = {
name: "alvin",
age: 18
}; --b 数值前自减1var person = {
name: "alvin",
age: 18
}; b=b-1
var person = {
name: "alvin",
age: 18
};
//赋值运算符
var person = {
name: "alvin",
age: 18
}; =
var person = {
name: "alvin",
age: 18
}; +=
var person = {
name: "alvin",
age: 18
}; -=
var person = {
name: "alvin",
age: 18
}; *=
var person = {
name: "alvin",
age: 18
}; /=
var person = {
name: "alvin",
age: 18
}; %=
var person = {
name: "alvin",
age: 18
}; **=
//比较运算符,比较的结果要么是true, 要么是false
var person = {
name: "alvin",
age: 18
};>var person = {
name: "alvin",
age: 18
}; 大于
var person = {
name: "alvin",
age: 18
};<var person = {
name: "alvin",
age: 18
}; 小于
var person = {
name: "alvin",
age: 18
};>=var person = {
name: "alvin",
age: 18
};大于或者等于
var person = {
name: "alvin",
age: 18
};<=var person = {
name: "alvin",
age: 18
};小于或者等于
var person = {
name: "alvin",
age: 18
};!=var person = {
name: "alvin",
age: 18
};不等于[计算数值]
var person = {
name: "alvin",
age: 18
};==var person = {
name: "alvin",
age: 18
};等于[计算]
var person = {
name: "alvin",
age: 18
};!== 不全等[不仅判断数值,还会判断类型是否一致]
var person = {
name: "alvin",
age: 18
};=== 全等[不仅判断数值,还会判断类型是否一致]
//逻辑运算符
var person = {
name: "alvin",
age: 18
};&&var person = {
name: "alvin",
age: 18
}; 并且var person = {
name: "alvin",
age: 18
};andvar person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};两边的运算结果为true,最终结果才是true
var person = {
name: "alvin",
age: 18
};||var person = {
name: "alvin",
age: 18
}; 或者var person = {
name: "alvin",
age: 18
};orvar person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
}; 两边的运算结果为false,最终结果才是false
var person = {
name: "alvin",
age: 18
};!var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};非var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};notvar person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};运算符的结果如果是true,则最终结果是false ,反之亦然.
var person = {
name: "alvin",
age: 18
};//逻辑运算符进阶用法:
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
}; 1. 实现短路
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var a = false || 2var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};>>> a = 2
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var a = true && "hehe"var person = {
name: "alvin",
age: 18
};>>>var person = {
name: "alvin",
age: 18
};a = "hehe"
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
}; 2. 快速布尔化[把数据快速转换成布尔类型]
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var a = 100
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};!!avar person = {
name: "alvin",
age: 18
};>>> true
//条件运算符[三目运算符]
条件?true:false
例如:
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var age = 12;
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var ret = age>=18?"成年":"未成年"; // 相当于 python中的"成年" if age >= 18 else "未成年"
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};console.log(ret);
*/6、流程控制语句
编程语言的流程控制分为三种：
[*]顺序结构(从上向下顺序执行)
[*]分支结构
[*]循环结构
之前我们学习的方式就是顺序执行，即代码的执行从上到下，一行行分别执行。
例如：
console.log("星期一");
console.log("星期二");
console.log("星期三");4.6.1、分支结构
[*]if 分支语句
if(条件){
// 条件为true时,执行的代码
}
if(条件){
// 条件为true时,执行的代码
}else{
// 条件为false时,执行的代码
}
if(条件1){
// 条件1为true时,执行的代码
}else if(条件2){
// 条件2为true时,执行的代码
}....
}else{
// 上述条件都不成立的时候,执行的代码
}
[*]switch语句
switch(条件){
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};case 结果1:
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
}; 满足条件执行的结果是结果1时,执行这里的代码..
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
}; break;
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};case 结果2:
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
}; 满足条件执行的结果是结果2时,执行这里的代码..
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
}; break;
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};.....
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};default:
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
}; 条件和上述所有结果都不相等时,则执行这里的代码
var person = {
name: "alvin",
age: 18
}; }1、switch比if else更为简洁
2、执行效率更高。switch…case会生成一个跳转表来指示实际的case分支的地址，而这个跳转表的索引号与switch变量的值是相等的。从而，switch…case不用像if…else那样遍历条件分支直到命中条件，而只需访问对应索引号的表项从而到达定位分支的目的。
3、到底使用哪一个选择语句，代码环境有关，如果是范围取值，则使用if else语句更为快捷；如果是确定取值，则使用switch是更优方案。
4.6.2、循环语句
[*]while循环
var person = {
name: "alvin",
age: 18
}; while(循环的条件){
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};// 循环条件为true的时候,会执行这里的代码
var person = {
name: "alvin",
age: 18
}; }
var person = {
name: "alvin",
age: 18
};循环案例：
var count = 0
while (count<10){
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
}; console.log(count);
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
}; count++;
}不同于python，js代码在运行时，会分为两大部分———预编译 和 执行阶段。
[*]预编译：会先检测代码的语法错误，进行变量、函数的声明。
[*]执行阶段：变量的赋值、函数的调用等，都属于执行阶段。
11.3、函数参数
（1） 参数基本使用
var person = {
name: "alvin",
age: 18
};
var person = {
name: "alvin",
age: 18
}; // 循环三要素
var person = {
name: "alvin",
age: 18
}; for(1.声明循环的开始; 2.条件; 4. 循环的计数){
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};// 3. 循环条件为true的时候,会执行这里的代码
var person = {
name: "alvin",
age: 18
}; }
var person = {
name: "alvin",
age: 18
};
var person = {
name: "alvin",
age: 18
}; for(循环的成员下标 in 被循环的数据){
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};// 当被循环的数据一直没有执行到最后下标,都会不断执行这里的代码
var person = {
name: "alvin",
age: 18
}; }var person = {
name: "alvin",
age: 18
}; （2）函数中的arguments对象
// 方式1
for (var i = 0;i<10;i++){
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};console.log(i)
}
// 方式2
var arr =
for (var i in arr){
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};console.log(i,arr)
}11.4、函数返回值
在函数体内，使用 return 语句可以设置函数的返回值。一旦执行 return 语句，将停止函数的运行，并运算和返回 return 后面的表达式的值。如果函数不包含 return 语句，则执行完函数体内每条语句后，返回 undefined 值。
for (var i = 0;i<100;i++){
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};if (i===88){
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};continuevar person = {
name: "alvin",
age: 18
};// 退出当次循环
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};// breakvar person = {
name: "alvin",
age: 18
};// 退出当前整个循环
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};}
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};console.log(i)
}1、在函数体内可以包含多条 return 语句，但是仅能执行一条 return 语句
2、函数的参数没有限制，但是返回值只能是一个；如果要输出多个值，可以通过数组或对象进行设计。
11.5、匿名函数
匿名函数，即没有变量名的函数。在实际开发中使用的频率非常高！也是学好JS的重点。
创建方式1:
var arrname = [元素0,元素1,….];var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};// var arr=;
创建方式2:
var arrname = new Array(元素0,元素1,….); // var test=new Array(100,"a",true);使用匿名函数表达式时，函数的调用语句，必须放在函数声明语句之后！
11.6、函数作用域
作用域是JavaScript最重要的概念之一，想要学好JavaScript就需要理解JavaScript作用域和作用域链的工作原理。
任何程序设计语言都有作用域的概念，简单的说，作用域就是变量可访问范围，即作用域控制着变量与函数的可见性和生命周期。在JavaScript中，变量的作用域有全局作用域和局部作用域两种。
var arr = ["A","B","C","D"];
// 内置属性
console.log( arr.length );
// 获取指定下标的成员
// console.log( arr ); // D
console.log( arr ); // 最后一个成员
// (1) pop()var person = {
name: "alvin",
age: 18
};出栈,删除最后一个成员作为返回值
var arr = ;
var ret = arr.pop();
console.log(arr); //
console.log(ret); // 5
// (2) push() 入栈,给数组后面追加成员
var arr = ;
arr.push("a");
console.log(arr); //
// (3) shift是将数组的第一个元素删除
var arr = ;
arr.shift()
console.log(arr); //
// (4) unshift是将value值插入到数组的开始
var arr = ;
arr.unshift("yuan")
console.log(arr); // ["yuan",1,2, 3, 4, 5]
// (5) reverse() 反转排列
var arr = ;
arr.reverse();
console.log(arr); //
// (6) slice(开始下标,结束下标)var person = {
name: "alvin",
age: 18
};切片,开区间
// (7) sort() 排序
var arr = ;
console.log( arr ); //
arr.sort();
//
// // 这是字符的排序,不是数值的排序
console.log(arr);var person = {
name: "alvin",
age: 18
}; //var person = {
name: "alvin",
age: 18
};
// 数值升序
var arr = ;
arr.sort(function(a,b){
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};return a-b;
});
console.log(arr);var person = {
name: "alvin",
age: 18
};//
// 数值降序
var arr = ;
arr.sort(function(a,b){
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};return b-a;
});
console.log(arr); //
// (8) splice(操作位置的下标,删除操作的成员长度,"替换或者添加的成员1","替换或者添加的成员2")var person = {
name: "alvin",
age: 18
};添加/删除指定的成员var person = {
name: "alvin",
age: 18
}; "万能函数"
var arr1 = ;
arr1.splice(1,1);
console.log(arr1); // 删除指定的1个成员var person = {
name: "alvin",
age: 18
};
var arr2 = ["a","b","c","d"];
arr2.splice(2,0,"w","x","w"); // 添加
console.log(arr2); // ["a", "b", "w", "x", "w", "c", "d"]
var arr3 = ["a","b","c"];
arr3.splice(1,1,"w");
console.log(arr3); // ["a", "w", "c"]
// (9) concat() 把2个或者多个数组合并
var arr1 = ;
var arr2 = ;
var ret = arr1.concat(arr2);
console.log( ret );
// (10) join()var person = {
name: "alvin",
age: 18
};把数组的每一个成员按照指定的符号进行拼接成字符串
var str = "广东-深圳-南山";
var arr = str.split("-");
console.log( arr ); // ["广东", "深圳", "南山"];
var arr1 = ["广东", "深圳", "南山"];
var str1 = arr1.join("-");
console.log( str1 ); // 广东-深圳-南山
// (11) find()var person = {
name: "alvin",
age: 18
};高阶函数, 返回符合条件的第一个成员
var arr = ;
var func = (num)=>{
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};if(num%2===0){
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};return num;
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};}
};
var ret = arr.find(func);
console.log( ret ); // 4
// (12)var person = {
name: "alvin",
age: 18
};filter() 高阶函数, 对数组的每一个成员进行过滤,返回符合条件的结果
var arr = ;
function func(num){var person = {
name: "alvin",
age: 18
};// 也可以使用匿名函数或者箭头函数
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};if(num%2===0){
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};return num;
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};}
}
var ret = arr.filter(func);var person = {
name: "alvin",
age: 18
};// 所有的函数名都可以作为参数传递到另一个函数中被执行
console.log( ret );
// (13) map() 对数组的每一个成员进行处理,返回处理后的每一个成员
var arr = ;
var ret = arr.map((num)=>{
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};return num**3;
});
console.log( retvar person = {
name: "alvin",
age: 18
};); //
// (14) 其它方法
// includesvar person = {
name: "alvin",
age: 18
}; 查询指定数据是否在数组中存在!
// indexOf()var person = {
name: "alvin",
age: 18
};查询指定数据在数组中第一次出现的位置
// isArray()var person = {
name: "alvin",
age: 18
};判断变量的值是否是数组
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
}; 首先熟悉下var
var arr =
for (var i in arr){
var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
}; console.log(i,arr)
}作用域案例：
var person = new Object();
person.name = "alvin";
person.age = 18;11.7、JS的预编译
js运行三个阶段：
[*]语法分析
[*]预编译
[*]解释执行
语法分析就是JS引擎去检查你的代码是否有语法错误，解释执行就是执行你的代码。最重要最需要理解的就是第二个环节预编译，简单理解就是在内存中开辟一些空间，存放一些变量与函数 。
预编译可分为全局预编译和局部预编译。
[*]在js脚本加载之后，会先通篇检查是否存在低级错误；
[*]在语法检测完之后，便进行全局预编译；
[*]在全局预编译之后，就解释一行，执行一行；
[*]当执行到函数调用那一行前一刻，会先进行函数预编译，再往下执行。
全局预编译的3个步骤：
[*]创建GO对象（Global Object）全局对象，即window对象。
[*]找变量声明，将变量名作为GO属性名，值为undefined
[*]查找函数声明，作为GO属性，值赋予函数体
局部预编译的4个步骤：
[*]创建AO对象（Activation Object）执行期上下文。
[*]找形参和变量声明，将变量和形参名作为AO属性名，值为undefined
[*]将实参值和形参统一。
[*]在函数体里面找函数声明，值赋予函数体。
GO对象是全局预编译，所以它优先于AO对象所创建和执行
案例分析：
var person = {
name: "alvin",
age: 18
};全局预编译
GO/window = {var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};a: undefined,var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};c: undefined，var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};foo: function(a) {var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};console.log(a);var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var a = 123;var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};console.log(a);var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};function a() {}var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};console.log(a);var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var b = function() {}var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};console.log(b);var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};function d() {}var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};}}解释执行代码（直到执行调用函数foo(20)语句）
GO/window = {var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};a: 10,var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};c: function (){var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};console.log("I at C function");var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};}var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};test: function(a) {var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};console.log(a);var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var a = 123;var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};console.log(a);var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};function a() {}var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};console.log(a);var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var b = function() {}var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};console.log(b);var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};function d() {}var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};}}调用函数foo(20)前发生布局预编译
// 局部预编译前两步：AO = {var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};a:undefined,var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};b:undefined,}// 局部预编译第三步：AO = {var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};a:20,var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};b:undefined,}// 局部预编译第四步：AO = {var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};a:function a() {},var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};b:undefinedvar person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};d:function d() {}}预编译总结：
[*]函数声明整体提升-(具体点说，无论函数调用和声明的位置是前是后，系统总会把函数声明移到调用前面）
[*]变量 声明提升-(具体点说，无论变量调用和声明的位置是前是后，系统总会把声明移到调用前，注意仅仅只是声明，所以值是undefined）
面试题：
var num3 = 10;function func3(){var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};console.log(num3);var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
}; var num3 = 20;var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
}; }func3();console.log(num3);var person = {
name: "alvin",
age: 18
};/*var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};// 全局编译var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};GO{var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
}; num3:undefined,var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
}; func3: function (){var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};console.log(num3);var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var num3 = 20;var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};}var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};// 全局执行var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var num3 = 10;var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};GO{var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
}; num3:10,var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
}; func3: function (){var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};console.log(num3);var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var num3 = 20;var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};}var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};// 局部编译var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};func3.AO{var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
}; num3:undefined,var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};}var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};// 局部执行var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};func3.AO{var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
}; num3:20,var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};}var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};// 全局执行var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};GO.num3 = 10var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};var person = {
name: "alvin",
age: 18
};}*/
来源:https://www.cnblogs.com/sbhglqy/p/18168077
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