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前端知识——编程形式有哪些

2020年02月14日 web前端 ⁄ 共 1943字 ⁄ 字号 评论关闭

  前端知识点——编程形式有哪些?

  bianchengxingshi:mianxiangguochenghemianxiangduixiang。

  前端知识点——typeof的类型

  typeofyouliuzhongshujuleixing:number,string,boolean,undefined,object,function。

  shuzu duixiang nulldetypeofdejieguodoushiobject;

  var num = [];

  console.log(typeof (num)); //jieguoshiobject;

  weishengmingdebianliangzhijiediaoyonghuibaocuo,tishi is not defined。

  ruguoshishiyongtypeof(weishengmingdebianliang),zejieguojiushibuhuibaocuo,danshijieguohuishiundefined;

607的彩的正确网址  typeof(weishengmingdebianliang)jieguojiushiundefined;

607的彩的正确网址  erqiezheigeundefinedshizifuchuanleixingde。

607的彩的正确网址  typeof(typeof(weishengmingdebianliang)),jieguojiushi string;

  lianxi:

  alert(typeof(a))//jieguojiushi string

  alert(typeof(undefined))//jieguojiushi string

  alert(typeof(nan))//jieguojiushi numer

  alert(typeof(null))//jieguojiushi object

  alert(typeof(nan))//jieguojiushinumber

  var a = '123abc';alert(typeof(+a));//jieguojiushinumber

607的彩的正确网址  alert(typeof(!!a));//jieguojiushi boolean

  alert(typeof(a + ''));//jieguojiushistring

  alert(1 == '1');//jieguojiushi true;

607的彩的正确网址  alert(nan == nan);//jieguojiushifalse;

607的彩的正确网址  alert(nan == undefined);//jieguojiushifalse;

  alert('11' + 11);//jieguojiushi 1111;

607的彩的正确网址  alert(1 === '1');//jieguojiushifalse;

  alert(parseint('123abc'));//jieguojiushi123;

  var num = 123123.345789;alert(num.tofixed(3));//jieguojiushi 123123。346;

  前端知识点——类型转换

  xianshileixingzhuanhuan

  number(mix):

  parseint(string,radix);

607的彩的正确网址  parsefloat(string);

607的彩的正确网址  tostring(radix);

  string(mix);

607的彩的正确网址  boolean();

  null zhuanhuanchengshuzidejieguoshi 0;

  true zhuanhuanchengshuzidejieguoshi 1;

607的彩的正确网址  false zhuanhuanchengshuzidejieguoshi 0;

  undefined zhuanhuanchengshuzidejieguoshi nan;

  parseint();jiangkuohaoneideneirongzhuanhuachengzhengxing;

  ruguoshifeishudeneirong,douhuizhuanhuanchengnan;

607的彩的正确网址  liru: true false undefined null douhuizhuanhuachengnan;

607的彩的正确网址  parseint(num,radix);

607的彩的正确网址  parseint()yougedutedetedian,nenggoucongshuziweikaishikan,zhidaofeishuziweijiezhi。

  suoyiparseint(‘123abc’)dejieguoshi123,qieshinumberleixingde123;

607的彩的正确网址  tostring();jiangcanshuzhuanhuachengzifuchuan。

  undefined he null meiyou tostring() fangfa

  隐式类型转换

  isnan()

607的彩的正确网址  ++ – + - (yiyuanzhengfu)

  +

  / %

  && || !

  < > <= >=

  == !=

  juli:

607的彩的正确网址  isnan(nan) true;

607的彩的正确网址  isnan(‘123’) false;

607的彩的正确网址  isnan(‘abc’) true;

  isnan(null) false

  number(null) = 0;

  number(undefined = nan);

  number(‘a’) == nan;

  < > = 都会进行隐式类型转化

607的彩的正确网址  undefinedjinxingnumber(),jisuandejieguojiushi:nan,nanbudengyurenhedongxi,baokuotabenshen。

  undefined == null;

  nan != nan;

  qianduanzhishidian——parseint yu tostring

  parseint();shijiangduiyingjinzhideshuzizhuanhuachengshijinzhi;

  tostring(); shijiangshijinzhideshuzizhuanhuachengduiyingdejinzhi;

  juli:

  jiang2jinzhideshuzhuanhuawei16jinzhi:

607的彩的正确网址  silujiushi,xianjiang2jinzhishuzhuanhuaweishijinzhishu,tongguo parseint();

607的彩的正确网址  ranhoujiangshijinzhideshuzhuanhuawei16jinzhideshu,tongguotostring();

607的彩的正确网址  var num = 10101010;

  var test = parseint(num,2);

607的彩的正确网址  console.log(test.tostring(16));

  parseint(canshu,jinzhijidi);jiangduiyingjidideshuzhuanhuachengshijinzhi

  tostring(mubiaojinzhi);jiangshijinzhidecanshuzhuanhuachengmubiaojinzhi。

baoqian!pinglunyiguanbi.

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