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数据类型
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‎数据类型初识/0.各种数据类型.js‎

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console.log(typeof "hello");//console.log()控制台输出内容
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console.log(typeof 222);//"number"
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console.log(typeof '222');//"string"
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console.log(typeof false);
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console.log(typeof "false");//这个上面的都是基本数据类型/
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console.log(typeof null);//object//object function 是引用数据类型；
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console.log(typeof {});
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console.log(typeof function () {});//function
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//变量是数据的代言人；
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var demoStr="hello";
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console.log("-----------------------");
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console.log(typeof demoStr);//string
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demoStr=22;//不推荐这么做 ；
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console.log(typeof demoStr);//number
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//typeof 总是返回string类型的； typeof()
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console.time("123");
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console.log("+++++++++++++++++++++");
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console.log(typeof (typeof "hello"));
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console.log(typeof (typeof 222));
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console.log(typeof typeof '222');
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console.log(typeof typeof false);
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console.log(typeof typeof "false");
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console.log(typeof typeof null);
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console.log(typeof typeof {});
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console.log(typeof typeof function () {});
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console.timeEnd("123");
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console.assert(1==1,"打脸了");
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var aloneVal=Symbol();
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console.log(typeof aloneVal);//symbol 存在的意义，避免多人开发时，变量覆盖；

‎数据类型初识/1.String.js‎

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//string 单引号'' / 双引号""包裹的内容
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/*alert(typeof "22");
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alert(typeof '22');
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alert(typeof "");
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alert(typeof '');*/
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console.log(typeof "22");
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console.log(typeof '2');
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console.log(typeof '');
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console.log(typeof "");
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console.log(typeof "false");
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console.log(typeof "null");
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//length,一般作为用户输入店名/用户名的长度限制；需要注意双字符精准度的问题；
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var str="123123123123123123123123123123";
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var chinaStr="哈喽";//双字节，不精确 4字节；
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console.log(str.length);
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console.log(chinaStr.length);//2
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//字符串创建的原理；
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var str1="12345";//把"12345"这个字符串赋值给str1这个变量；
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str1="1234";//把"1234"这个字符串赋值给str1这个变量；
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/*
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* 并不是把"12345"修改为"1234"然后赋值给str1
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*
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* */
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console.log(str1);//"1234"
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console.log('1"23\'4\n56\'78');
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// alert("1213123\naaaaaa")
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//toString方法；
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//22 - > "22"
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console.log(typeof 22);
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console.log(typeof (22).toString());
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var testStr=22+"";//隐式调用toString方法
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console.log(typeof 22+"");//+ - * / 2*2+10
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console.log(typeof testStr);//2*(2+10)
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//eval()
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console.log("00000000000000000");
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console.log(eval("22+12"));//"22+12" -> 22+12 ->34
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//
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console.log("**********************");
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console.log(typeof (22+""));//string 22 -> "22"
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console.log(typeof (+"22"));//"22" -> 22 单目运算符+
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console.log([1,2,3,4]+"");//1,2,3,4
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console.log("**********************");
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console.log("1.1" + 1.1);
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console.log(+"1.1" + 1.1);
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console.log((+"1.1") + (+1.1));

‎数据类型初识/2.Number.js‎

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//正数，负数，零，NaN都是属于Number
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// ***NaN -> Not a Number不是一个数，但是属于数字类型；**
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console.log(typeof 222);
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console.log(typeof 222.22);
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console.log(typeof -10);
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console.log(typeof -10.34);
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console.log(typeof 0);
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console.log(typeof -0);
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//NaN
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console.log((22*"aa"));//NaN number
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console.log(typeof (22*"aa"));//number
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console.log(22==22);//true 单个等于号是赋值的意思； Invalid left-hand side in assignment
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//== 两个等于号才是判断；
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console.log((22*"aa")==(22*"bb"));//false
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console.log((22*"aa")==22);//false
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//inNaN
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console.log(isNaN(22*"aa"));//true (22*"aa")计算出的值不是一个数，对吗？ 对；
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console.log(isNaN(22));// 22这个值不是一个数，对吗？ 不对； false (NaN -> Not a Number不是一个数，)
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//number的转换方法； 别的数据类型转为数字类型；(不一定是字符串)
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/* 五种 转为数字的；
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* +"22" 字符串转为数字；
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* "22"-0
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* Number()
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* parseInt()
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* parseFloat()
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* */
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console.log("+++++++++++++++++++++++++");//隐式
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console.log(+"22");//隐式
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console.log(Number("22"));//显式 22
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console.log(Number(false));//显式 ->0
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console.log(Number(true));//显式 ->1
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console.log(Number(null));//显式 -> 0
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console.log(Number(undefined));//显式 NaN
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console.log(Number({}));//显式
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console.log(Number("22.22"));
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console.log(Number("22.22a"));//失败了 NaN
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console.log(parseInt("22.22a"));//22
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console.log(parseFloat("22.22a222"));//22.22
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console.log(parseFloat("22.22.22"));//22.22
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// + - * /
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console.log(("++++++++"));
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console.log(13%10); //13/10 3 多余的3 会被输出
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console.log(5%3);//2
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var time=623648364569346563463;//time单位是秒；转为X分X秒；
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var minis=parseInt(time/60);//保存是分钟
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var second=time%60;//3
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var targetVal=minis+"分"+second+"秒";
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console.log(" minis:"+minis+" second:"+second);
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console.log(targetVal);
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//小练习：
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/*
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* var time=623648364569346563463;//time是怎么得到的》当前的服务器时间 - 双11 这个阶段多少秒；
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* 是多少天，多少小时，多少分钟，多少秒；
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* */
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console.log("***********************");
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console.log("22"-1);//"22" -> 22 -> (22-1) -> 21
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console.log("22"-0);

‎数据类型初识/3.Boolean.js‎

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var a=52;
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var b=30;
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function demoBoolean(a, b) {
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if (a>b){//2>30 -> false
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console.log(a+" 大于 " +b)
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}else if(a==b){//2==30 -> false
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console.log(a+" 等于 " +b)
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}else{
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console.log(a+" 小于 " +b)
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}
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console.log(a>b);
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console.log(a==b);
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if(null){
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console.warn("条件为真的时候才输出")
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}else{
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console.warn("if条件为假的时候才输出")
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}
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}
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demoBoolean(a,b);
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/*
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* 如果a>B； ->"a的值"大于"b的值"
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* 如果a==B；->"a的值"等于"b的值"
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* 如果a<B；->"a的值"小于"b的值"
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*
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* */
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/* ................................非常重要。。。。。。。。。。
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* 哪些值是false（false本身）
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* 数字：0、-0 、NaN、
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* 字符串：''（空字符串）
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* null 、
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* undefined、
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* */
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console.log("---------------------------------");
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console.log(Boolean(0)); //false
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console.log(Boolean(-0)); //false
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console.log(Boolean(1)); //true
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console.log(Boolean(-5)); //true
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console.log(Boolean("222"));//true
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console.log(Boolean('')); //false 空的字符串
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console.log(Boolean(" ")); //true 包含空格的字符串
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console.log("---------------------------------");
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console.log(Boolean("0"));//true
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console.log(Boolean(null));//false
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console.log(Boolean(undefined));//false
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console.log(Boolean({}));//true
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console.log(Boolean(function () {}));//true
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console.log(Boolean(false));//false
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console.log("---------------------------------");
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console.log(Boolean(55*"asd"));// NaN false
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// ! !!
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console.log("************************");
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console.log(Boolean(0));//false
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console.log(Boolean(!0));//true
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console.log(!0);//true 原理: 0 隐式的调用Boolean方法Boolean(0) -> false -> !false ->true
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console.log(!!0);// !(!false)->!true ->false

‎数据类型初识/4.null和undefined.js‎

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// var NULL=2;
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console.log(typeof null);//object 这是一个空的指针；
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console.log(typeof NULL);// NULL- >undefined
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//结果是undefined 除了用在typeof外，会报错；
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console.log(undefined*15);//NaN
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// console.log(undefined*aa);//aa is not defined
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// console.log(NULL+15);//NULL is not defined 相当于NULL 这个变量没有找到；
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//
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var js;
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console.log(js);//undefined
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console.log(typeof undefined);//undefined
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console.log(typeof typeof undefined);//string
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//null和undefined比较
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/*
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* === 相同比较，首先判断是否是同一个类型；不是的话，直接false；
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* == 比较是否相等；(如果是不一样的类型，会转为相同的类型，然后再进比较)
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* */
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console.log(null == null);//true
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console.log(null == undefined);//true
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console.log(undefined == undefined);//true
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console.log(undefined === undefined);//true
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console.log(null === undefined);//false null->Null undefined -> Undefined
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console.log(false == 0);//true false->0 0==0? true
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console.log(Number("22") == 22);//true "22"隐士的调用Number->22 -> 22== 22 -> true
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console.log("---------------------------");
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console.log(null == 1);//false
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console.log(null == "2312312");//false
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console.log(null == false);//false
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console.log(null == 0);//false
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console.log(null == "");//false
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console.log(null == NaN);//false
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console.log("++++++++++++++++++++++++++");
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console.log(undefined == 1);//false
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console.log(undefined == "2312312");//false
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console.log(undefined == false);//false
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console.log(undefined == 0);//false
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console.log(undefined == "");//false
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console.log(undefined == NaN);//false
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//应用场景经常出现在 做定时器的时候；
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var timer=null;
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// 对象的属性
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var oDemo={
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// aaa:"这是oDemo的aaa值"
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};
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oDemo.bbb="Hello";
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console.log(oDemo.aaa);//undefined
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console.log(oDemo.bbb);//Hello
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//ByIn
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var oDiv1=document.getElementById("div1"),
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oDiv2=document.getElementById("div2");
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console.log(oDiv1);
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console.log(oDiv2);//null
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//function 返回值 默认是undefined；
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function demo() {
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return;
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}
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var aDemo=demo();
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console.log(aDemo);//undefined

‎数据类型初识/5.Object.js‎

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var num=2;
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console.dir(num);//number 实例
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console.dir(num.__proto__);//Number 类
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/*
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*
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* constructor :Object
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*
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*
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* */
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var str="haha";
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console.dir(str);//string 实例
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console.dir(str.__proto__);//String 类
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/*判断是否一致*/
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console.log(num.__proto__.__proto__=== str.__proto__.__proto__);//true
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//万物皆对象,并不等于只有一个对象类型的；
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// Number / String / Object / Boolean
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//key:value
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//1、字面量的创建方式；推荐的方式
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var o={
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name:"zhu",
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say:"hello"
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};
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console.log(o);//{name: "zhu", say: "hello"}
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var oDemo={};
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// oDemo.name1=
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if(!oDemo.flagVal){
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oDemo.flagVal="Test"
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}
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oDemo.name="bang";
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oDemo.say="hahahahahahahha";
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console.log(oDemo.flagVal);//Test
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console.log(oDemo);//{flagVal: "Test", name: "bang", say: "hahahahahahahha"}
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//new
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var demo1=new Object();//不推荐的使用方法；
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demo1.haha="hahahahahahah";
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console.log(demo1);//{haha: "hahahahahahah"}
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//jQuery的AJAX；
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/*var options={
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url:"babababab",
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type:"",
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date:{}
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};
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$.ajax(options);*/
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function Test(opt) {
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//bala bala
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}
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var testVal=Test({a:"",b:""});
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//Array;
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var a=[1,2,3,4,5,6,7];//var a=[1,2,3,4,5,6,7,] 低版本浏览器，length的;
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console.log(a);//编程语言里，index是以0为开始的；
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console.log("第一位,a[0]",a[0]);
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console.log(a[1]);
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console.log(a.length);//7
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// -> //

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