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对象

Object#

let a =new Object()

增#

a.name='xiaoyu'a.age=22a.sex='men'a['height']=180  //两种方式congsole.log(a)//{ name: 'xiaoyu', age: 22, sex: 'men' ,height: 180 }

查#

console.log(a.name)console.log(a['name'])//两种都可以console.log('day' in a)//查看是否有这个属性，没有就是false

对象的遍历#

let a ={user:'xiaoyu',pwd:"446688"}let b={user:'xiaoyu',pwd:"446688"}for(let i in a){    console.log(i,a[i]);}

结果：user xiaoyu

pwd 446688

删#

delete a.age delete a['age']//两种console.log(a)//{ name: 'xiaoyu', sex: 'men' }

改#

a.name='ruru'a['name']='ruru'//2z

禁止更改object.freeze#

let ak={  name:'xiaoyu',  age:22}Object.freeze(ak)//起到保护作用，禁止更改objectak.age=32console.log(ak);//输出{ name: 'xiaoyu', age: 22 }，g

对象的解构#

const people={    name:'xiaouyu',    age:33,    run:function(){        console.log('i am running');    }}let {name,age,run}=people  //里面的名称要和object的一样，填几个就解构几个console.log(name);//xiaouyuconsole.log(age);//33console.log(run);//[Function: run]run()//i am running
const people={  name:'xiaouyu',  age:33,  run:function(){      console.log('i am running');  }}let {name:a,age:b,run:c}=people  //也可以重新命名console.log(a);//xiaoyu

嵌套式对象解构

const LOCAL_FORECAST = {  yesterday: { low: 61, high: 75 },  today: { low: 64, high: 77 },  tomorrow: { low: 68, high: 80 }};//相当于要解构的名称替换那个ylet {yesterday: { low: lowToday, high},today: { low, high:highToday }}=LOCAL_FORECASTconsole.log(lowToday);

Math#

PI#

Math.PI

max,min#

console.log(Math.max(3,8,9))console.log(Math.min(8,9))

绝对值abs#

console.log(Math.abs(-9))

取整#

向下取整floor#

console.log(Math.floor(1.9))//结果1

向上取整ceil#

console.log(Math.ceil(1.1))//结果2

四舍五入round#

console.log(Math.round(1.4))//1console.log(Math.round(1.5))//2

random随机数#

Math.random()结果是0到1之间的小数

两个数之间的随机数#

function getRandom(min,max){    return Math.floor(Math.random()*(max-min+1))+min}

Date#

创建对象#

let a =new Date('2020-08-18')  //出现实际时间let b=new Date(2020,8,18)  //月份+1，日期-1let c=new Date()  //本地时间//2020-08-18T00:00:00.000Z//2020-09-17T16:00:00.000Z//2021-08-19T13:00:50.121Z

返回时间总毫秒数

let a =+new Date()//1629378392009

string#

索引#

indexOf#

let a ='xiaoyuxiaoyu'console.log(a.indexOf('a',3))//8    indexof(x,3)从index3开始查找字符所在的索引，无字符返回-1

lastIndexOf#

let a ='xiaoyuxiaoyu'console.log(a.lastIndexOf('a',9))//从第几个位置开始往前找，8

反索引#

charAt#

let a ='xiaoyuxiaoyu'console.log(a.charAt(2))//a,返回index=2的字符

charCodeAt#

let a ='xiaoyuxiaoyu'console.log(a.charCodeAt(2))//返回所在位置的ASCLL码，97

下标#

let a ='xiaoyuxiaoyu'console.log(a[2])//a,直接下标就可以了

字符串链接#

concat#

let a ='xiaoyu'let b='is'let c='beautiful'
console.log(a.concat(b,c))

截取字符串#

substr#

let a ='xiaoyu'console.log(a.substr(1,5))//从第几个开始截取，取多少个  iaoyu

替换replace#

replace

let a ='xiaoyu'console.log(a.replace('x','ruru'))//前面是要替换的，字符，后面是替换成的字符

注意只会替换第一个查找到的字符

分隔成数组#

let a ='xiaoyux'console.log(a.split('|'))

以什么来分割，如果没有就不好分割，如果是''，就每一个字符为数组的元素

字符串转数字#

parseInt#

parseInt(*string*, *radix*) 解析一个字符串并返回指定基数的十进制整数， radix 是2-36之间的整数，表示被解析字符串的基数。

  • string

    要被解析的值。如果参数不是一个字符串，则将其转换为字符串(使用 ToString 抽象操作)。字符串开头的空白符将会被忽略。

  • radix 可选

    从 2 到 36，表示字符串的基数。例如指定 16 表示被解析值是十六进制数。请注意，10不是默认值！