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ES6-ES13学习笔记（4.0）

news 2025/8/23 18:29:33

includes函数判断字符串是否存在指定字符

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<body><script>let myname="kunkun"console.log(myname.includes("ku"))console.log(myname.includes("a"))console.log(myname.includes("u",2))//传第二个参数，以指定索引开头进行查找console.log(myname.startsWith("k"))console.log(myname.endsWith("n"))//end的第二个参数是从后往前的索引console.log(myname.repeat(2))console.log(myname.repeat(2.3))console.log(myname.repeat(0))</script>
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startsWith函数判断自发货窜是否以指定的字符串开头

endsWith函数判断字符串是否以指定的字符串结尾

repeat函数重复字符串（默认是重复一次。如果传入的参数为0，那么就会输出空字符串）

ES6支持了二进制，八进制的转换

2. Number.isFinite Number.isNaN

它与传统的全局方法isFinite()和isNaN()的区别在于，传统方法先调用Number()将非数值的值转为数值，再进行判断，而这两个新方法支队数值有效，Number.isFinite()对于非数值一律返回false，Number.isNaN()只对NaN返回true，非NaN一律返回false

Number.isInteger 判断是否为整数

3.极小常量 Number.EPSILON

4.取整(舍弃小数部分) Math.trunc

5.Math.sign判断一个数是正数、负数、还是零。对于非数值，会首先转换为数值

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<body><script>//1 二进制，八进制写法let num1=100let num2=0x12let num3=0b0101let num4=0o1210console.log(num1)console.log(num2)console.log(num3)console.log(num4)//2. Number.isFinite Number.isNaNlet num5=Number.isFinite(100)//truelet num6=Number.isFinite(100/0)//falselet num7=Number.isFinite(Infinity)//falselet num8=Number.isFinite("1")//falseconsole.log(num8)let num9=Number.isNaN(100)let num10=Number.isNaN(NaN)let num11=Number.isNaN("Infinity")let num13=Number.isNaN("mez")let num12=Number.isNaN("100")console.log(num9)console.log(num10)console.log(num11)console.log(num12)console.log(num13)let num14=Number.isInteger(100)let num15=Number.isInteger(100.00)let num16=Number.isInteger("Infinity")let num17=Number.isInteger("mez")let num18=Number.isInteger("100")console.log(num14)console.log(num15)console.log(num16)console.log(num17)console.log(num18)//3.极小常量function isEqual(x,y){return Math.abs(x-y)<Number.EPSILON}console.log(isEqual(5,6))console.log(isEqual(0.1+0.2,0.3))console.log(Number.EPSILON)//4.取整(舍弃小数部分)console.log(Math.trunc(1.8))console.log(Math.trunc(1.1))console.log(Math.trunc(-1.8))console.log(Math.trunc(-1.1))//Math.sign判断一个数是正数、负数、还是零。对于非数值，会首先转换为数值console.log(Math.sign(-100))console.log(Math.sign(100))console.log(Math.sign("-100"))console.log(Math.sign(0))console.log(Math.sign("mez"))</script>
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